[Add]: Groups component explanations

[imath]

What needs to be done?

This documentation page just like #210 #212 or #214 needs to be located into a components directory of the user docs and only deal with this component feature. For instance, the activity page is belonging to the activity component and should be documented into this component unlike what is done into this codex page. New documentation should talk about group types and group roles (using content from this other codex page)

Handbook to add the page in

buddypress/docs/user

Tasks to accomplish

• This task has been added to the "Todo" panel of the Documentation project.
• A PR has been submitted to the BuddyPress GH repository, it has been linked to this issue/task & the task was moved to the "In progress" panel of the Documentation project.
• The PR has been converted to a SVN patch and committed to the BuddyPress SVN repository & the task was moved to the "Done" panel of the Documentation project.