Instructions for the release process (#137)

* Instructions for the release process

* Breaking changes are minor releases since still below version 1.0

RELEASE.md

@@ -0,0 +1,22 @@
+# dbt-codegen releases
+
+## When do we release?
+There's a few scenarios that might prompt a release:
+
+| Scenario                                   | Release type |
+|--------------------------------------------|--------------|
+| Breaking changes to existing macros        | minor        |
+| New functionality                          | minor        |
+| Fixes to existing macros                   | patch        |
+
+## Release process
+
+1. Begin a new release by clicking [here](https://github.com/dbt-labs/dbt-codegen/releases/new)
+1. Click "Choose a tag", then paste your version number (with no "v" in the name), then click "Create new tag: x.y.z. on publish"
+    - The “Release title” will be identical to the tag name
+1. Click the "Generate release notes" button
+1. Copy and paste the generated release notes into `CHANGELOG.md`, commit, and merge into the `main` branch
+1. Click the "Publish release" button
+    - This will automatically create an "Assets" section containing:
+        - Source code (zip)
+        - Source code (tar.gz)