Installation of Picard from according to the instructions supplied in the CONTRIBUTING.md file create an extra build directory named 'picard.egg-info'. Since this directory is not cloned directly from the remote repo and is created when building and installing the repo, it should ideally be added to the `.gitignore` file.
Fixed by https://github.com/metabrainz/picard/commit/41243420c90184089c9d60710e11bccba2b6695e