README: clarify weekly call

Weekly call is for all OCI projects and per discussion on today's call,
updates to indicate the call is for all OCI projects (rather than having
multiple calls.)

And updates time zone description from PST/PDT to Pacific time

Signed-off-by: Rob Dolin <RobDolin@microsoft.com>

README.md

@@ -72,7 +72,7 @@ When in doubt, start on the [mailing-list](#mailing-list).
 
 ## Weekly Call
 
-The contributors and maintainers of the project have a weekly meeting Wednesdays at 10:00 AM PST.
+The contributors and maintainers of all OCI projects have a weekly meeting Wednesdays at 10:00 AM (USA Pacific.)
 Everyone is welcome to participate via [UberConference web][UberConference] or audio-only: 646-494-8704 (no PIN needed.)
 An initial agenda will be posted to the [mailing list](#mailing-list) earlier in the week, and everyone is welcome to propose additional topics or suggest other agenda alterations there.
 Minutes are posted to the [mailing list](#mailing-list) and minutes from past calls are archived to the [wiki](https://github.com/opencontainers/runtime-spec/wiki) for those who are unable to join the call.