Update README.md

add usage instructions

Author: qno

README.md

@@ -2,3 +2,16 @@
 Example repository for building and publishing a VCV Rack plugin with GitHub Actions.
 
 ![Build VCV Rack Plugin](https://github.com/qno/vcv-plugin-github-actions-example/workflows/Build%20VCV%20Rack%20Plugin/badge.svg)
+
+___
+
+### How to build a VCVRack plugin with Github Action
+
+1. In your plugin repository create a folder `.github/workflows`
+2. Put the workflow definition [build-plugin.yml](https://github.com/qno/vcv-plugin-github-actions-example/blob/main/.github/workflows/build-plugin.yml) into this folder
+3. Make changes to your sources and push them to Github
+4. In your Github repository navigate into the Action tab to see the progress and status of the Workflow run
+5. To create a Github Release that contains the built plugin for all platforms you need to create and push a tag, e.g. like this:
+   * `git tag v2.0.9 -m "create v2.0.9"`
+   * `git push origin --tags`
+   * **Note:** Make sure that your tag version number is the same as the version in the [plugin.json](https://github.com/qno/vcv-plugin-github-actions-example/blob/main/plugin.json#L4) and the tag starts with v (it is a convention), otherwise the the publish step will be canceled.