chore: add example

Author: felangel

packages/dart_frog_lint/example/README.md

@@ -1 +1,11 @@
-# Example
+# Dart Frog Lint
+
+1. Install `dart_frog_lint`
+
+   `dart pub add --dev dart_frog_lint`
+
+1. Add an `analysis_options.yaml` to the root of your project with the recommended rules
+
+   ```yaml
+   include: package:dart_frog_lint/recommended.yaml
+   ```