Say plainly that stats cover all teams

The README said stats were "not team-scoped by the server", which reads
as though they were unscoped. They are scoped, to all of the caller's
teams (TestTeams_AlertsAndStatsAreScoped in terdut-server); what they
cannot do is narrow to one. Docs only, no code change.

README.md

@@ -32,8 +32,8 @@ The schedule is one team's rota, so the Schedule section shows the active team,
 or with *all* showing the first team you own. Only a team's owners, and
 administrators, can change its rota; anyone else gets the reason in the status
 bar instead of a picker. The picker offers only that team's members, because the
-server refuses anybody else. Stats are not team-scoped by the server and always
+server refuses anybody else. Stats always cover all your teams; the server
-cover all your teams.
+cannot narrow them to one.
 
 Administrators are the only users who can create or delete users, or act on
 someone else's password, topic or API keys. Everyone can manage their own.