update README

Author: HarryGogonis

README.md

@@ -1 +1,24 @@
 # GitHub Action for Kustomize Build+Diff
+
+Example Usage
+```yaml
+name: kustomize-diff
+on:
+  pull_request:
+jobs:
+  kustomize-diff:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+    - uses: supplypike/kustomize-diff@v1
+      id: kustdiff
+      with:
+        kustomizations: |-
+          .kustomization/staging
+          .kustomization/production
+    - uses: mshick/add-pr-comment@v2
+      with:
+        message: ${{ steps.kustdiff.outputs.diff }}
+```