Add Github workflow to check for changelog entry

When creating PR we should update the changelog as this helps others see
what is upcoming in the next release and makes release Alaveteli
versions easier.

This workflow ensures an `docs/CHANGES.md` is modified or the pull
request description contains `[skip changelog]`

Update the PR template to help remind devs to do this before the PR is
created.

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,3 +9,7 @@
 ## Screenshots
 
 ## Notes to reviewer
+
+<hr>
+
+Have you updated the changelog? If this is not necessary, put square brackets around this: skip changelog

.github/workflows/changelog.yml

@@ -0,0 +1,40 @@
+name: Changelog
+
+on:
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - reopened
+      - edited
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+
+    env:
+      GH_TOKEN: ${{ github.token }}
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v3
+
+    - name: Check for [skip changelog]
+      run: |
+        PR_DESCRIPTION=$(gh pr view https://github.com/${{ github.repository }}/pull/${{ github.event.pull_request.number }} --json body -q '.body')
+        if echo "$PR_DESCRIPTION" | grep -q "\[skip changelog\]"; then
+          echo "Skip changelog found in PR description. Passing the action."
+          exit 0
+        fi
+
+    - name: Check for changes in doc/CHANGES.md
+      run: |
+        git fetch origin ${{ github.event.pull_request.base.ref }}
+        FILES_CHANGED=$(git diff --name-only origin/${{ github.event.pull_request.base.ref }} ${{ github.sha }})
+        if [[ "$FILES_CHANGED" == *"doc/CHANGES.md"* ]]; then
+          echo "doc/CHANGES.md has been modified. Passing the action."
+          exit 0
+        else
+          echo "doc/CHANGES.md has not been modified. Failing the action."
+          exit 1
+        fi