Package categories are used by an automated bot, cms-bot, to notify coordinators of different areas. These are defined in cms-bot/categories.py.
In particular:
CMSSW_L2: defines a mapping between github users and a given category.CMSSW_CATEGORIES: defines a mapping between github categories and packages
associated to it.In order to add a new package, just update the relevant categories in
CMSSW_CATEGORIES and do a pull request. A package can belong to multiple
categories.
While github allows you to be notified for changes to a repository, you might want to be notified just for an handful of packages. This can be done by adding yourself as a watcher of a specific packege. This is controlled by the watchers.yaml file. In order to watch a package, add your github username and a list of package names or a regular expression matching the packages you would like to watch.