(doc) Hint about integration test in PR template

Closes #123
diff --git a/.github/pull_request_template.md b/.github/pull_request_template.md
index c04497b..9cd2e76 100644
--- a/.github/pull_request_template.md
+++ b/.github/pull_request_template.md
@@ -13,6 +13,7 @@
  - [ ] Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
  - [ ] Run `mvn clean verify` to make sure basic checks pass. A more thorough check will 
        be performed on your pull request automatically.
+ - [ ] You have run the integration tests successfully (`mvn -Prun-its clean verify`).
 
 If your pull request is about ~20 lines of code you don't need to sign an
 [Individual Contributor License Agreement](https://www.apache.org/licenses/icla.pdf) if you are unsure