chore: update readme

Author: Salakar

README.md

@@ -7,14 +7,60 @@
 
 ---
 
-TODO
+## Usage
 
-**Example annotation output**:
+```yaml
+name: "analyze"
+on: # rebuild any PRs and main branch changes
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  dart: # make sure the action works on a clean machine without building
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: dart-lang/setup-dart@v1
+      - uses: invertase/github-action-dart-analyzer@v1
+        with:
+          # (Optional) Treat info level issues as fatal.
+          fatal-infos: false
+
+          # (Optional) Treat warning level issues as fatal
+          # (defaults to true).
+          fatal-warnings: false
+
+          # (Optional) Whether to add annotations to GitHub actions summary / PR
+          # review files.
+          # (defaults to true).
+          annotate: true
+
+          # (Optional) If set to true only annotations will be created and the
+          # GitHub action itself will not fail on Dart analyzer problems. 
+          # (defaults to false).
+          annotate-only: false
+
+          # (Optional) The working directory to run the Dart analyzer in 
+          # (defaults to `./`).
+          working-directory: ./
+```
+
+
+## Screenshots
+
+**Example annotation output in PR changes review**:
 
 1) ![image](https://user-images.githubusercontent.com/5347038/149161220-dbd92743-2cdc-4083-b7f2-31ed9ca7f855.png)
 2) ![image](https://user-images.githubusercontent.com/5347038/149161397-d6a72437-a15f-4dbb-a6b5-227bd11da210.png)
 3) ![image](https://user-images.githubusercontent.com/5347038/149161493-66e2b7f6-177a-4daa-bb66-9d0a26ba391d.png)
 
+**Example annotation output in check summary**:
+
+![image](https://user-images.githubusercontent.com/5347038/149163192-e7f97894-cd1c-4892-92be-580f121a9aef.png)
+
+
 **Example workflow logs output**:
 
 ![image](https://user-images.githubusercontent.com/5347038/149162346-573bf836-489f-458f-8501-60148d2104cd.png)