[Migrate]: How To Join a Private Group

[imath]

Link to the existing BP Codex page.

https://codex.buddypress.org/member-guide/how-to-join-a-private-group/

What needs to be done?

A unique page should explain how to join:

• a private group
• an hidden group (being invited)
• a public group

Screenshots need to be updated!

Handbook to migrate the page in

buddypress/docs/user

Tasks to accomplish

• [x] This task has been added to the "Todo" panel of the Documentation project.
• [x] The corresponding line of the data/README.md Pages list has been marked as "Migrate issue/task created".
• [x] 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.
• [x] 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.

[vapvarun]

Doc Preview: https://github.com/vapvarun/BuddyPress/blob/join-private-group/docs/user/administration/groups/join-private-group.md