Add instructions on how to install a local version of the annotations repo

[angelhof]

A common usecase is that a user needs to experiment with new commands and therefore needs to update annotations. Currently annotations are downloaded from PyPI and therefore it is hard to play with a local version of the library. We should add instructions on how to locally install and work with a local branch of annotations. Ideally, we could also add a script that helps with that (in addition to instructions).

[angelhof]

PR #750 tries to address this!