(chore) automatic greeting for users first contrib (#2385)

.github/workflows/greetings.yml

@@ -0,0 +1,26 @@
+name: Greetings
+
+on: [pull_request, issues]
+
+jobs:
+  greeting:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/first-interaction@v1
+      with:
+        repo-token: ${{ secrets.GITHUB_TOKEN }}
+#        issue-message: 'Message that will be displayed on users'' first issue'
+        pr-message: >
+          Thank you so much for your first contribution!  It's appreciated.
+          One of our maintainers will review it as soon as they can.
+          
+          If you didn't modify `CHANGES.md` already, please go and do that now and push a second
+          commit.  The `CHANGES.md` file is where we keep a running summary of changes so users 
+          know what to expect when we issue periodic releases.
+          
+          Again, thanks.
+          
+          ---
+          
+          If by some chance you're just chomping at the bit to make a second PR we do have a "beginner friendly" tag:
+          https://github.com/highlightjs/highlight.js/labels/beginner%20friendly