Document calendar summary icons

Summary:
Fixes T11809. Ref

  - Explicitly document the summary icon hints -- I don't think these are too hard to figure out (and maybe this stuff should just go in the tooltips) but we can start here.
  - Use color + shape to distinguish between "cancelled" and "declined", not just color (for users with vision accessibility issues).
  - Translate a "minute(s)" string into sensible English.
  - Use RSVP status on the month view green circle thing.

Test Plan:
  - Read docs.
  - Looked at month view.
  - Read reminder mail.
  - Viewed month view mobile view.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11809

Differential Revision: https://secure.phabricator.com/D16872

src/docs/user/userguide/calendar.diviner

@@ -37,6 +37,22 @@ revision or task.
 You can click through to a user's profile to see more details about their
 availability.
 
+Status Icons
+============
+
+On the month and day views, Calendar shows an icon next to each event to
+indicate status. The icons are:
+
+  - {icon user-plus, color=green} **Invited, Individual**: You're personally
+    invited to the event.
+  - {icon users, color=green} **Invited, Group**: A project you are a member
+    of is invited to the event.
+  - {icon check-circle, color=green} **Attending**: You're attending the event.
+  - {icon times-circle, color=grey} **Declined**: You've declined the event.
+  - {icon times, color=red} **Cancelled**: The event has been cancelled.
+
+If you don't have any special relationship to the event and the event does not
+have any special status, an event-specific icon is shown instead.
 
 Importing Events
 ================