Add an example to the README.md.

Author: jemc

README.md

@@ -1,3 +1,47 @@
 # `savi-lang/action-build-release`
 
 Build Savi application release binaries for multiple platforms from a single CI runner.
+
+## Example
+
+If you have a repository with a Savi application manifest named `my-app`, then you could use a workflow like this one to give a workflow that can be triggered manually at any time to tag a new release and upload release binaries as assets attached to the release:
+
+```yaml
+name: release
+
+on:
+  workflow_dispatch:
+    inputs:
+      version-tag:
+        description: |
+          The name of the version to release (e.g. `v1.2.3` or `v0.20220131.0`).
+        required: true
+
+jobs:
+  all:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: savi-lang/action-install@v1.0.0
+
+      # Build the release binaries for all platforms and package in tarballs.
+      - uses: savi-lang/action-build-release@v1
+        id: my-app
+        with:
+          manifest-name: my-app
+          tarball-name: my-app-${{ github.event.inputs.version-tag }}
+          all-platforms: true
+          macosx-accept-license: true
+          windows-accept-license: true
+
+      # Tag the new release and upload the files from the tarball directory.
+      - uses: softprops/action-gh-release@v1
+        if: ${{ github.event.inputs.version-tag != '' }}
+        with:
+          tag_name: ${{ github.event.inputs.version-tag }}
+          generate_release_notes: true
+          token: ${{ secrets.BOT_GITHUB_TOKEN }} # (allows triggering workflows)
+          fail_on_unmatched_files: true
+          files: |
+            ${{ steps.my-app.outputs.tarball-directory }}/*
+```