Updated readme to include github action example (transcend-io#38)

Co-authored-by: dmattia <david@transcend.io>

README.md

@@ -22,6 +22,44 @@ This tool creates Atlantis YAML configurations for Terragrunt projects by:
 
 This is especially useful for organizations that use monorepos for their Terragrunt config (as we do at Transcend), and have thousands of lines of config.
 
+## Installation and Usage
+
+Recommended: Install any version via go get:
+
+```bash
+cd && GO111MODULE=on go get github.com/transcend-io/terragrunt-atlantis-config@master && cd -
+```
+
+Alternative: Install a stable versions via Homebrew:
+
+```bash
+brew install transcend-io/tap/terragrunt-atlantis-config
+```
+
+Usage:
+
+```bash
+# From the root of your repo
+terragrunt-atlantis-config generate
+
+# or from anywhere
+terragrunt-atlantis-config generate --root /some/path/to/your/repo/root
+
+# output to a file
+terragrunt-atlantis-config generate --autoplan --output ./atlantis.yaml
+
+# enable auto plan
+terragrunt-atlantis-config generate --autoplan
+
+# define the workflow
+terragrunt-atlantis-config generate --workflow web --output ./atlantis.yaml
+
+# ignore parent terragrunt configs (those which don't reference a terraform module)
+terragrunt-atlantis-config generate --ignore-parent-terragrunt
+```
+
+Finally, check the log output (or your output file) for the YAML.
+
 ## Extra dependencies
 
 For 99% of cases, this tool can sniff out all dependencies in a module. However, you may have times when you want to add in additional dependencies such as:
@@ -56,43 +94,38 @@ In your `atlantis.yaml` file, you will end up seeing output like:
   dir: example-setup/extra_dependency
 ```
 
-## Installation and Usage
-
-Recommended: Install any version via go get:
-
-```bash
-cd && GO111MODULE=on go get github.com/transcend-io/terragrunt-atlantis-config@master && cd -
-```
+## Auto Enforcement with Github Actions
 
-Alternative: Install a stable versions via Homebrew:
+It's a best practice to require that `atlantis.yaml` stays up to date on each Pull Request.
 
-```bash
-brew install transcend-io/tap/terragrunt-atlantis-config
-```
+To make this easy, there is an open-source Github Action that will fail a status check on your PR if the `atlantis.yaml` file is out of date.
 
-Usage:
+To use it, add this yaml to a new github action file in your repo:
 
-```bash
-# From the root of your repo
-terragrunt-atlantis-config generate
-
-# or from anywhere
-terragrunt-atlantis-config generate --root /some/path/to/your/repo/root
-
-# output to a file
-terragrunt-atlantis-config generate --autoplan --output ./atlantis.yaml
-
-# enable auto plan
-terragrunt-atlantis-config generate --autoplan
-
-# define the workflow
-terragrunt-atlantis-config generate --workflow web --output ./atlantis.yaml
-
-# ignore parent terragrunt configs (those which don't reference a terraform module)
-terragrunt-atlantis-config generate --ignore-parent-terragrunt
+```yaml
+name: terragrunt-atlantis-config
+on:
+  push:
+    paths:
+    - '**.hcl'
+    - '**.tf'
+    - '**.hcl.json'
+
+jobs:
+  terragrunt_atlantis_config:
+    runs-on: ubuntu-latest
+    name: Validate atlantis.yaml
+    steps:
+      - uses: actions/checkout@v2
+      - name: Ensure atlantis.yaml is up to date using terragrunt-atlantis-config
+        id: atlantis_validator
+        uses: transcend-io/terragrunt-atlantis-config-github-action@v0.0.3
+        with:
+          version: v0.5.0
+          extra_args: '--autoplan --parallel=false
 ```
 
-Finally, check the log output (or your output file) for the YAML.
+You can customize the version and flags you typically pass to the `generate` command in those final two lines.
 
 ## Contributing