Add Git section to the contributing page
diff --git a/src/main/jbake/content/contributing.md b/src/main/jbake/content/contributing.md
index 1296751..108b7bd 100644
--- a/src/main/jbake/content/contributing.md
+++ b/src/main/jbake/content/contributing.md
@@ -47,6 +47,26 @@
works and how its projects are structured - and don't hesitate to ask on our
[mailing lists](http://sling.apache.org/project-information.html#mailing-lists)!
+### Git
+
+#### Commit meesages
+
+For non-trivial commits a Jira issue is required. Once the Jira issue is created, the commit message must include the Jira issue key
+and the summary as the first line, followed by an optional description of the fix. For example:
+
+```
+SLING-1234 - Fix NPE in FooImpl
+
+When the FooImpl is reconfigured the bar field can be set to null, so check
+against null values.
+```
+
+#### Pull request changes
+
+When iterating on a GitHub pull request a single commit can receive multiple follow-up fixes. To help preserve
+a linear history and to make changes easy to follow, please squash the changes in a single commit and force-push
+to the GitHub branch.
+
### Testing
Each Sling module comes with an automated build, usually based on Apache Maven. Your change should be covered
