chore: update release process in contributing docs (#445)

Author: kevinsamoei

CONTRIBUTING.md

@@ -21,7 +21,26 @@ Lastly, open a pull request on Github.
 
 ## Releasing
 
-1. Merge the release PR
-2. Switch to the default branch `git checkout main`
-3. Pull latest changes `git pull`
-4. Publish the package `npm publish`
+This repo uses [semantic versioning](https://semver.org/) with the help of [release-please](https://github.com/googleapis/release-please). 
+We use [release-please](https://github.com/googleapis/release-please) workflow for releases. The [workflow](./.github/workflows/release-please.yml) is responsible for:
+
+- Creating release PRs
+- Once release PRs are merged it:
+	- creates a release [tag](https://github.com/netlify/netlify-plugin-lighthouse/releases)
+	- publishes the new version to [npm](https://www.npmjs.com/package/@netlify/plugin-lighthouse)
+	- creates an update PR in [plugins](https://github.com/netlify/plugins)
+
+Things to be aware of:
+
+- use [conventional commits](https://www.conventionalcommits.org/)
+- Only `feat` and `fix` commits will be released. `chore` commits will not create a release PR
+- To jump versions e.g `v2.0` to `v3.0` make sure to indicate that in your PR by having a `Release-As` in the commit message e.g `Release-As: 3.0.0`. See ["How do I change the version number?"](https://github.com/googleapis/release-please#how-do-i-change-the-version-number) docs in release-please.
+
+#### Steps
+
+1. Merge your feature or bug fix PR
+2. Release please creates a release PR
+3. Merge the release PR
+4. Verify that the new version is available in npm
+5. Go to plugins and merge the version update PR
+