documentation: usage example

README.md

@@ -2,6 +2,29 @@
 
 A GitHub Action to ensure that your PR title matches a given regex.
 
+## Usage
+
+Create a workflow definition at `.github/workflows/<my-workflow>.yml` with something like the following contents:
+
+```yaml
+name: PR Lint
+
+on:
+  pull_request:
+    types: [opened, edited, reopened]
+
+jobs:
+  pr-lint:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: morrisoncole/[email protected]
+      with:
+        title-regex: "#EX-[0-9]+"
+        on-failed-regex-comment: "This is just an example. Failed regex: `%regex%`!"
+        repo-token: "${{ secrets.GITHUB_TOKEN }}"
+
+```
+
 ## Related Reading
 
 * [GitHub Action Metadata Syntax](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/metadata-syntax-for-github-actions)