Merge pull request #4 from oscal-club/chore-update-readme

Update README for release.

README.md

@@ -1,2 +1,25 @@
 # oscal-cli-action
+
 A GitHub Action to process, convert, and validate OSCAL content with the NIST oscal-cli tool.
+
+# Usage
+
+**NOTE**: This is a composite action for the GitHub Actions and you must check
+the code and setup a Java runtime as dependencies, or it will fail.
+
+```yaml
+- name: Checkout
+  uses: actions/checkout@755da8c3cf115ac066823e79a1e1788f8940201b
+  id: checkout
+- name: Setup Java
+  uses: actions/setup-java@c3ac5dd0ed8db40fedb61c32fbe677e6b355e94c
+  with:
+    distribution: adopt
+    java-version: 11
+  id: setup_java
+- name: Run oscal-cli for version check (debugging on)
+  uses: oscal-club/[email protected]
+  with:
+    args: ssp validate repo/path/to/ssp.xml
+  id: convert_ssp
+```