Add action to warn against PR against master (should be develop)

.github/workflows/master_branch_pr.yml

@@ -7,6 +7,13 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
+      - name: 'Comment PR'
+        uses: actions/github-script@0.3.0
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const { issue: { number: issue_number }, repo: { owner, repo }  } = context;
+            github.issues.createComment({ issue_number, owner, repo, body: 'Hello world ! 👋' });
       - name: Post PR comment
         uses: mshick/add-pr-comment@v1
         with: