docs: flesh out releasing.html

Properly document the whole process:
 - Brief on what, when, where
 - Picking, testing, branchpoints, pre-release announcement
 - Releasing, announcement, website and bugzilla updates

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
2 files changed