updated usage

README.md

@@ -18,6 +18,39 @@ steps:
 - run: flutter build apk
 ```
 
+Use latest release for particular channel:
+
+```yaml
+steps:
+- uses: actions/checkout@v1
+- uses: actions/setup-java@v1
+  with:
+    java-version: '12.x'
+- uses: subosito/flutter-action@v1
+  with:
+    channel: 'stable' # or: 'dev' or 'beta'
+- run: flutter pub get
+- run: flutter test
+- run: flutter build apk
+```
+
+Use latest release for particular version and/or channel:
+
+```yaml
+steps:
+- uses: actions/checkout@v1
+- uses: actions/setup-java@v1
+  with:
+    java-version: '12.x'
+- uses: subosito/flutter-action@v1
+  with:
+    version: '1.7.x'
+    channel: 'dev' # optional
+- run: flutter pub get
+- run: flutter test
+- run: flutter build apk
+```
+
 Matrix Testing:
 
 ```yaml