feat(deprecated): add deprecation message (#907)

Author: bcoe

README.md

@@ -1,5 +1,7 @@
 # Standard Version
 
+> **`standard-version` is deprecated**. If you're a GitHub user, I recommend [release-please](https://github.com/googleapis/release-please) as an alternative. I encourage folks to fork this repository and, if a fork gets popular, I will link to it in this README.
+
 A utility for versioning using [semver](https://semver.org/) and CHANGELOG generation powered by [Conventional Commits](https://conventionalcommits.org).
 
 ![ci](https://github.com/conventional-changelog/standard-version/workflows/ci/badge.svg)