Automatically comment if a PR doesn't meet the style guide (#453)

Author: 17cupsofcoffee

.github/workflows/ci.yml

@@ -1,6 +1,9 @@
 name: Zola
 
-on: [push, pull_request]
+on:
+  push:
+    branches: source
+  pull_request:
 
 jobs:
   zola:
@@ -18,6 +21,17 @@ jobs:
       with:
         args: '.'
         config: '.markdownlint.json'
+    - name: Comment if lints failed
+      if: failure() && github.base_ref # base_ref is only set for PRs 
+      uses: actions/github-script@v3
+      with:
+        script: |
+          github.issues.createComment({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+              body: "It looks like the MarkdownLint checks for this PR have failed. Please take a look at the 'Checks' tab to see what needs changing."
+          });
     - name: Install Zola
       run: curl -L ${BASE_URL}/${VERS}/zola-${VERS}-${ARCH}.tar.gz | tar -xz
     - run: ./zola --version