Show gem groups/extensions/plugins

[marcoroth]

There are gems which are meant to be used with each other, either because the extend or build on top of another gem.

There should be a way to configure/relate gems to each other and show it in the docs.

A good example might be the rubocop gem, since it's allowed to be used with a bunch of extensions:

• rubocop-rails
• rubocop-performance
• rubocop-minitest
• rubocop-rspec
• ...

Or the rails gem, which is meant to be used with all it's subgems:

• activerecord
• activesupport
• actioncontroller
• actioncable
• ...

[marcoroth]

Some ideas