feat: adds support for releases from alternate paths (#50)

Refs: googleapis/release-please#501

README.md

@@ -40,6 +40,8 @@ Automate releases with Conventional Commit Messages.
 | `release-type` | What type of project is this a release for? Reference [Release types supported](#release-types-supported); new types of releases can be [added here](https://github.com/googleapis/release-please/tree/master/src/releasers) |
 | `package-name` | A name for the artifact releases are being created for (this might be the `name` field in a `setup.py` or `package.json`) |
 | `bump-minor-pre-major` | Should breaking changes before 1.0.0 produce minor bumps?  Default `No` |
+| `--path`          | create a release from a path other than the repository's root |
+| `--monorepo-tags` | add prefix to tags and branches, allowing multiple libraries to be released from the same repository. |
 
 | output | description |
 |:---:|---|