CI: Run markdown linter on pull requests

...so that main branch builds to not fail unexpectedly after merging a PR from a fork.

Author: armsnyder

.github/workflows/markdown-lint.yml

@@ -1,6 +1,6 @@
 name: Markdown lint
 
-on: push
+on: [push,pull_request]
 
 jobs:
   markdown-lint:
@@ -9,4 +9,4 @@ jobs:
       - uses: actions/checkout@v2
       - uses: avto-dev/markdown-lint@v1
         with:
-          args: 'docs'
+          args: 'docs'