feat: Set up markdownlint GitHub Action for automated linting (Closes #14) (#42)

* Adds lint.yaml with linting instructions for changed MD files

* Updates contributing.md with automated linting information

* Instructions to check details for automated check fail

* Update CONTRIBUTING.md to include lint URLs

Co-authored-by: Elizabeth Campolongo <[email protected]>

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Elizabeth Campolongo <[email protected]>

Author: 3 people

.github/workflows/lint.yaml

@@ -0,0 +1,31 @@
+name: Linting
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+
+      # This identifies which files changed in the specific commit or PR
+      - uses: tj-actions/changed-files@v47
+        id: changed-files
+        with:
+          files: '**/*.md'
+          separator: ","
+
+      # This runs the linter ONLY on the files identified above
+      - uses: DavidAnson/markdownlint-cli2-action@v22
+        if: steps.changed-files.outputs.any_changed == 'true'
+        with:
+          globs: ${{ steps.changed-files.outputs.all_changed_files }}
+          separator: ","

CONTRIBUTING.md

@@ -177,7 +177,12 @@ chore: update mkdocs dependencies
 
 ### Linting
 
-The project uses [markdownlint](https://github.com/DavidAnson/markdownlint) with configuration in `.markdownlint.json`. Key settings:
+The project uses [markdownlint](https://github.com/DavidAnson/markdownlint) with configuration in `.markdownlint.json`.
+
+**Automated Checks:**
+We have a GitHub Action that checks for formatting errors on Pull Requests. To follow best practices, **it only checks files that you have modified.** If the check fails, click the **Details** link next to the status check to view the error logs and see exactly what needs fixing.
+
+**Key Rules:**
 
 - 4-space indentation for lists (`MD007`).
 - No hard tab restrictions disabled.
@@ -186,7 +191,8 @@ The project uses [markdownlint](https://github.com/DavidAnson/markdownlint) with
 - Allowed code blocks without language specification (`MD040`).
 - Allow fenced code blocks, as this commonly errors when indented (see [discussion](https://github.com/DavidAnson/markdownlint/issues/327)).
 
-For faster PR review, you may want to run linting locally; we do have a PR Action in place as well. First install markdownlint, then run
+**Local Testing**
+For faster PR review, you may want to run linting locally. We recommend installing [`markdownlint-cli`](https://github.com/igorshubovych/markdownlint-cli) or the [VS Code extension](https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint).
 
 ```console
 markdownlint -c .markdownlint.json -f docs/wiki-guide/