ci: Trigger pipeline for pull requests

.github/workflows/ci.yml

@@ -1,7 +1,17 @@
 name: GitHub CI
 
-# Execute this for every push
-on: [push]
+# When to execute
+on:
+  push:
+    # Pushes to important branches
+    branches:
+      - develop
+      - main
+    # Release tags
+    tags:
+      - v*
+  # Any pull request
+  pull_request:
 
 # Use bash explicitly for being able to enter the conda environment
 defaults:

CONTRIBUTING.md

@@ -61,6 +61,11 @@ To contribute follow these steps:
     This also works if you pushed to a fork instead of the main repository.
     Add a description and explanation of your changes and work through the pull request author checklist provided.
     Feel free to request reviews from specific team members.
+
+    **NOTE:** If a pull request originates from a fork, a team member (usually the reviewer) will have to [approve workflow runs](https://docs.github.com/en/actions/how-tos/manage-workflow-runs/approve-runs-from-forks).
+    Before doing so, please carefully check the suggested changes for potentially harmful code.
+    If unsure, ask the core developers.
+
 9.  After approval of the pull request, the branch is merged into `develop` and your changes will become part of the next CLIMADA release.
 
 ## Resources