Add versioning information to README (#26)

* add description of how we version

* improve wording

Author: apmatthews

README.md

@@ -120,3 +120,9 @@ jobs:
 * [Storing secrets in GitHub repositories](https://docs.github.com/en/actions/reference/encrypted-secrets)
 * It is recommended to leverage one of [WP Engine's .gitignore templates.](https://wpengine.com/support/git/#Add_gitignore)
 * This action excludes several files and directories from the deploy by default. See the [exclude.txt](https://github.com/wpengine/github-action-wpe-site-deploy/blob/main/exclude.txt) for reference.
+
+## Versioning
+
+We follow [SemVer](https://semver.org/) and [GitHub's action versioning recommendations](https://github.com/actions/toolkit/blob/01e1ff7bc04e1c57c980a0d1530478a5b60cf812/docs/action-versioning.md) for maintaining major, minor, and patch [version tags](https://github.com/wpengine/github-action-wpe-site-deploy/tags). Patch tags (e.g. `v1.1.1`) are created for each release and will not move once created. Major tags (e.g. `v1`) and minor tags (e.g. `v1.1`) will be updated to track their respective latest versions.
+
+We recommend binding this action to the latest major tag so that you will receive backwards compatible updates.