[Add]: Sitewide Notices

[vapvarun]

What needs to be done?

Write a simple guide on how to use 'Sitewide Notices' in BuddyPress to send out important messages to everyone on the site, including tips on how to make these messages clear and helpful.

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.

[vapvarun]

Preview: https://github.com/vapvarun/BuddyPress/blob/site-notices-patch-1/docs/user/administration/users/site-notices.md
Branch: https://github.com/vapvarun/BuddyPress/tree/site-notices-patch-1

[emaralive]

@vapvarun & @imath ,

I'm going to edit this issue to reflect that this is really an "Add" as opposed to being a "Migrate", e.g., edit the title and remove some irrelevant information from the body (link to codex and checkbox related to data/README.md), unless there are objections. I'll wait a few days before making the edits.