PARQUET-1980: Add an info about Pull Requests' testing

* Add a line that PRs are automatically tested at GitHub Actions (for AMD64) and TravisCI (for ARM64).
* Replace the obsolete git-wip-us with gitbox
* minor Markdown improvements
diff --git a/output/contribute/index.html b/output/contribute/index.html
index 6e5a097..bd6736e 100644
--- a/output/contribute/index.html
+++ b/output/contribute/index.html
@@ -141,6 +141,7 @@
 <li>Submit the patch as a GitHub pull request against the master branch. For a tutorial, see the GitHub guides on forking a repo and sending a pull request. Prefix your pull request name with the JIRA name (ex: <a href="https://github.com/apache/parquet-mr/pull/5">https://github.com/apache/parquet-mr/pull/5</a>).</li>
 <li>Make sure that your code passes the unit tests. You can run the tests with <code>mvn test</code> in the root directory. </li>
 <li>Add new unit tests for your code. </li>
+<li>All Pull Requests are tested automatically on <a href="https://github.com/apache/parquet-mr/actions">GitHub Actions</a>. <a href="https://travis-ci.org/github/apache/parquet-mr">TravisCI</a> is also used to run the tests on ARM64 CPU architecture</li>
 </ol>
 
 <p>If you’d like to report a bug but don’t have time to fix it, you can still post it to our <a href="https://issues.apache.org/jira/browse/PARQUET">issue tracker</a>, or email the mailing list (<a href="mailto:dev@parquet.apache.org">dev@parquet.apache.org</a>).</p>
@@ -151,7 +152,7 @@
 
 <p>How to merge a Pull request (have an apache and github-apache remote setup):</p>
 <div class="highlight"><pre class="highlight plaintext"><code>git remote add github-apache git@github.com:apache/parquet-mr.git
-git remote add apache https://git-wip-us.apache.org/repos/asf/parquet-mr.git
+git remote add apache https://gitbox.apache.org/repos/asf?p=parquet-mr.git
 </code></pre></div>
 <p>run the following command</p>
 <div class="highlight"><pre class="highlight plaintext"><code>dev/merge_parquet_pr.py
@@ -168,20 +169,20 @@
 
 Proceed with merging pull request #3? (y/n): 
 </code></pre></div>
-<p>If this looks good, type y and hit enter.</p>
-<div class="highlight"><pre class="highlight plaintext"><code>From git-wip-us.apache.org:/repos/asf/parquet-mr.git
+<p>If this looks good, type <code>y</code> and hit enter.</p>
+<div class="highlight"><pre class="highlight plaintext"><code>From gitbox.apache.org:/repos/asf/parquet-mr.git
 * [new branch]      master     -&gt; PR_TOOL_MERGE_PR_3_MASTER
 Switched to branch 'PR_TOOL_MERGE_PR_3_MASTER'
 
 Merge complete (local ref PR_TOOL_MERGE_PR_3_MASTER). Push to apache? (y/n):
 </code></pre></div>
-<p>A local branch with the merge has been created. type y and hit enter to push it to apache master</p>
+<p>A local branch with the merge has been created. Type <code>y</code> and hit enter to push it to apache master</p>
 <div class="highlight"><pre class="highlight plaintext"><code>Counting objects: 67, done.
 Delta compression using up to 4 threads.
 Compressing objects: 100% (26/26), done.
 Writing objects: 100% (36/36), 5.32 KiB, done.
 Total 36 (delta 17), reused 0 (delta 0)
-To git-wip-us.apache.org:/repos/asf/parquet-mr.git
+To gitbox.apache.org:/repos/asf/parquet-mr.git
    b767ac4..485658a  PR_TOOL_MERGE_PR_X_MASTER -&gt; master
 Restoring head pointer to b767ac4e
 Note: checking out 'b767ac4e'.
@@ -203,7 +204,7 @@
 
 Would you like to pick 485658a5 into another branch? (y/n):
 </code></pre></div>
-<p>For now just say n as we have 1 branch</p>
+<p>For now just say <code>n</code> as we have 1 branch</p>
 
 <h2 id="website">Website</h2>
 
@@ -221,7 +222,7 @@
 <h3 id="make-changes-in-source">Make changes in source/</h3>
 
 <p>Make any changes in the source directory:</p>
-<div class="highlight"><pre class="highlight plaintext"><code>cd site/source/
+<div class="highlight"><pre class="highlight plaintext"><code>cd parquet-site/source/
 vim contribute.html.md
 </code></pre></div>
 <h3 id="generating-the-website">Generating the website</h3>
diff --git a/source/contribute.html.md b/source/contribute.html.md
index 10d88ce..3329cfa 100644
--- a/source/contribute.html.md
+++ b/source/contribute.html.md
@@ -10,6 +10,7 @@
   3. Submit the patch as a GitHub pull request against the master branch. For a tutorial, see the GitHub guides on forking a repo and sending a pull request. Prefix your pull request name with the JIRA name (ex: https://github.com/apache/parquet-mr/pull/5).
   4. Make sure that your code passes the unit tests. You can run the tests with `mvn test` in the root directory. 
   5. Add new unit tests for your code. 
+  6. All Pull Requests are tested automatically on [GitHub Actions](https://github.com/apache/parquet-mr/actions). [TravisCI](https://travis-ci.org/github/apache/parquet-mr) is also used to run the tests on ARM64 CPU architecture
 
 If you’d like to report a bug but don’t have time to fix it, you can still post it to our [issue tracker](https://issues.apache.org/jira/browse/PARQUET), or email the mailing list (dev@parquet.apache.org).
 
@@ -20,7 +21,7 @@
 How to merge a Pull request (have an apache and github-apache remote setup):
 
 	git remote add github-apache git@github.com:apache/parquet-mr.git
-	git remote add apache https://git-wip-us.apache.org/repos/asf/parquet-mr.git
+	git remote add apache https://gitbox.apache.org/repos/asf?p=parquet-mr.git
 
 run the following command
 
@@ -40,22 +41,22 @@
 
 	Proceed with merging pull request #3? (y/n): 
 
-If this looks good, type y and hit enter.
+If this looks good, type `y` and hit enter.
 
-	From git-wip-us.apache.org:/repos/asf/parquet-mr.git
+	From gitbox.apache.org:/repos/asf/parquet-mr.git
 	* [new branch]      master     -> PR_TOOL_MERGE_PR_3_MASTER
 	Switched to branch 'PR_TOOL_MERGE_PR_3_MASTER'
 
 	Merge complete (local ref PR_TOOL_MERGE_PR_3_MASTER). Push to apache? (y/n):
 
-A local branch with the merge has been created. type y and hit enter to push it to apache master
+A local branch with the merge has been created. Type `y` and hit enter to push it to apache master
 
 	Counting objects: 67, done.
 	Delta compression using up to 4 threads.
 	Compressing objects: 100% (26/26), done.
 	Writing objects: 100% (36/36), 5.32 KiB, done.
 	Total 36 (delta 17), reused 0 (delta 0)
-	To git-wip-us.apache.org:/repos/asf/parquet-mr.git
+	To gitbox.apache.org:/repos/asf/parquet-mr.git
 	   b767ac4..485658a  PR_TOOL_MERGE_PR_X_MASTER -> master
 	Restoring head pointer to b767ac4e
 	Note: checking out 'b767ac4e'.
@@ -77,7 +78,7 @@
 
 	Would you like to pick 485658a5 into another branch? (y/n):
 
-For now just say n as we have 1 branch
+For now just say `n` as we have 1 branch
 
 ## Website
 
@@ -96,7 +97,7 @@
 ### Make changes in source/
 Make any changes in the source directory:
 
-	cd site/source/
+	cd parquet-site/source/
 	vim contribute.html.md
 
 ### Generating the website