Setup markdownlint Github Action

.github/workflows/pr.yml

@@ -14,4 +14,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4
+    - name: Write git diff to temp file
+      run: |
+        git fetch origin
+        git diff origin/${{ github.base_ref }} --unified=0 *.md translations/*/*.md \
+        > ${{ runner.temp }}/diff.md
     - uses: DavidAnson/markdownlint-cli2-action@v17
+      with:
+        globs: "${{ runner.temp }}/diff.md"

.markdownlint.yaml

@@ -1,4 +1,3 @@
-# MD013/line-length
 MD013:
   line_length: 120
 
@@ -13,3 +12,6 @@ MD033: false
 
 # no-inline-html : Bare URL used (site should be attributed transparently, because otherwise we have to un-necesarily explain where the link directs)
 MD034: false
+
+# first-line-h1 : First line in a file should be a top-level heading (Ignore because diff file will never have valid heading)
+MD041: false