Document on how to use the dashboard.

In http://confluence.atlassian.com/display/CRUCIBLE/Using+the+Dashboard we don't describe to new users that "All Activity" only shows your activity until you start starring repos/directories or users.

So a new user will wonder why only their activity is displayed when logged in, but anonymous users see all activity on the dashboard.

see https://support.atlassian.com/browse/FSH-2515