repository.yml does not only live in the master branch

Hi,

I have found an inconsistency in [Identifying a Repo](https://github.com/apache/mynewt-documentation/blob/master/docs/tutorials/repo/add_repos.rst#identifying-a-repo)

It states that:

> the repository.yml file lives only in the master branch of the git repository

Looking at [Mynewt-core](https://github.com/apache/mynewt-core) we can see that `repository.yml` is present on several branches.

Is this an error in the core repo or in the doc?

Thanks

Read the “Identifying a Repo” section in docs/tutorials/repo/add_repos.rst and compare its repository.yml statement with the branches in the linked mynewt-core repository. Confirm whether the documentation or core repository is inconsistent, then update the documentation to describe the verified behavior.

Written by the indexing model from the issue text.