Add example workflow demonstrating linting only changed files (closes #12).

.github/workflows/changed.yml

@@ -0,0 +1,18 @@
+on: [push, pull_request]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        fetch-depth: 2
+    - uses: tj-actions/changed-files@v24
+      id: changed-files
+      with:
+        files: '**/*.md'
+        separator: "\n"
+    - uses: DavidAnson/markdownlint-cli2-action@v6
+      if: steps.changed-files.outputs.any_changed == 'true'
+      with:
+        globs: ${{ steps.changed-files.outputs.all_changed_files }}

README.md

@@ -97,6 +97,11 @@ To prevent linting issues from failing the workflow run:
 See [`example.yml`][example-yml] for a simple GitHub workflow that uses
 `markdownlint-cli2-action`.
 
+See [`changed.yml`][changed-yml] for a GitHub workflow that lints only the
+Markdown files that changed in the most recent commit (useful for Pull
+Requests and/or gradually introducing linting rules to a new repository).
+
+[changed-yml]: .github/workflows/changed.yml
 [command-line]: https://github.com/DavidAnson/markdownlint-cli2#command-line
 [commonmark]: https://commonmark.org/
 [example-yml]: .github/workflows/example.yml