[build.yaml options] README says `freezed:` but should be `freezed:freezed`

**Describe what scenario you think is uncovered by the existing examples/articles**
freezed config in `build.yaml` should be `freezed:freezed:` rather thran `freezed:`

**Describe why existing examples/articles do not cover this case**
See above

**Additional context**

[link](https://pub.dev/packages/freezed#changing-the-behavior-for-the-entire-project)
