README: Make meetings monthly (were weekly)

There was a call for making them as-needed:

On Wed, Aug 16, 2017 at 11:26:18AM -0400, Michael Crosby wrote [1]:
> I vote for canceling these.  We don't have the turnout anymore.
>
> We should go to an on-needed basis, where, if we have an agenda the
> maintainers of the project can schedule a meeting to discuss any
> pressing issues.  If not, lets not have a meeting for the sake of
> having a meeting.
>
> We can also rely on IRC more so that we can have an async
> conversation that is more convenient for others.

But we ended up going with monthly meetings:

On Wed, Aug 16, 2017 at 11:25:44AM -0500, Chris Aniszczyk wrote [2]:
> I'd prefer monthly if we had an option, it would be useful for some
> of us who are working on certification to at least have an avenue to
> meet with the dev team on a call, but it's up to the TDC to decide.

On Thu, Aug 17, 2017 at 06:24:04AM -0500, Chris Aniszczyk wrote [3]:
> So lets do Monthly, first Wed at 1700 PDT unless anyone objects

The ICS was validated with [4].

[1]: https://groups.google.com/a/opencontainers.org/d/msg/dev/PC2DzxarMqA/c_6gqsn1AQAJ
     Subject: Re: Do we have a ConCall tomorrow at 8am (Pacific)
     Date: Wed, 16 Aug 2017 11:26:18 -0400
     Message-ID: <CADe0Yksi_DM6eSEGhxGh8eF6ODxnY4sqEPiy4DQ0gNtdTEGYmw@mail.gmail.com>
[2]: https://groups.google.com/a/opencontainers.org/d/msg/dev/PC2DzxarMqA/_7CSvQf5AQAJ
     Subject: Re: Do we have a ConCall tomorrow at 8am (Pacific)
     Date: Wed, 16 Aug 2017 11:25:44 -0500
     Message-ID: <CAPon+wOC6gC_d95AEoxdAH_b58h7JoM=Utv6eUD8vijUZ5xd=A@mail.gmail.com>
[3]: https://groups.google.com/a/opencontainers.org/d/msg/dev/PC2DzxarMqA/SVF0KiY3AgAJ
     Subject: Re: Do we have a ConCall tomorrow at 8am (Pacific)
     Date: Thu, 17 Aug 2017 06:24:04 -0500
     Message-ID: <CAPon+wO2fR4yv5=JVGPcocfg4CA8is5a+0MEA3Lg1DQTJpUWeA@mail.gmail.com>
[4]: https://icalendar.org/validator.html

Signed-off-by: W. Trevor King <wking@tremily.us>

README.md

@@ -52,17 +52,12 @@ It also guarantees that the design is sound before code is written; a GitHub pul
 Typos and grammatical errors can go straight to a pull-request.
 When in doubt, start on the [mailing-list](#mailing-list).
 
-### Weekly Call
-
-The contributors and maintainers of all OCI projects have a weekly meeting on Wednesdays at:
-
-* 8:00 AM (USA Pacific), during [odd weeks][iso-week].
-* 2:00 PM (USA Pacific), during [even weeks][iso-week].
+### Meetings
 
+The contributors and maintainers of all OCI projects have monthly meetings at 5:00 PM (USA Pacific) on the first Wednesday of every month.
 There is an [iCalendar][rfc5545] format for the meetings [here](meeting.ics).
-
 Everyone is welcome to participate via [UberConference web][uberconference] or audio-only: +1 415 968 0849 (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.
+An initial agenda will be posted to the [mailing list](#mailing-list) in the week before each meeting, and everyone is welcome to propose additional topics or suggest other agenda alterations there.
 Minutes from past meetings are archived [here][minutes], with minutes from especially old meetings (September 2015 and earlier) archived [here][runtime-wiki].
 
 ### Mailing List

meeting.ics

@@ -20,30 +20,15 @@ TZNAME:PDT
 END:DAYLIGHT
 END:VTIMEZONE
 BEGIN:VEVENT
-UID:tdc-meeting-1@opencontainers.org
-DTSTAMP:20170405T220000Z
-DTSTART;TZID=America/Los_Angeles:20170329T080000
-RRULE:FREQ=WEEKLY;INTERVAL=2;BYDAY=WE
+UID:tdc-meeting@opencontainers.org
+DTSTAMP:20170817T150000Z
+DTSTART;TZID=America/Los_Angeles:20170906T170000
+RRULE:FREQ=MONTHLY;INTERVAL=1;BYDAY=1WE
 DURATION:PT1H
 SUMMARY:OCI TDC Meeting
 DESCRIPTION;ALTREP="https://github.com/opencontainers/runtime-spec#
- weekly-call":Open Containers Initiative Developer Meeting\n
- https://github.com/opencontainers/runtime-spec#weekly-call\n
- Web: https://www.uberconference.com/opencontainers\n
- Audio-only: +1 415 968 0849 (no PIN needed)
-LOCATION:https://www.uberconference.com/opencontainers
-URL:https://github.com/opencontainers/runtime-spec/blob/master/meeting.ics
-END:VEVENT
-BEGIN:VEVENT
-UID:tdc-meeting-2@opencontainers.org
-DTSTAMP:20170517T143500Z
-DTSTART;TZID=America/Los_Angeles:20170517T140000
-RRULE:FREQ=WEEKLY;INTERVAL=2;BYDAY=WE
-DURATION:PT1H
-SUMMARY:OCI TDC Meeting
-DESCRIPTION;ALTREP="https://github.com/opencontainers/runtime-spec#
- weekly-call":Open Containers Initiative Developer Meeting\n
- https://github.com/opencontainers/runtime-spec#weekly-call\n
+ meetings":Open Containers Initiative Developer Meeting\n
+ https://github.com/opencontainers/runtime-spec#meetings\n
  Web: https://www.uberconference.com/opencontainers\n
  Audio-only: +1 415 968 0849 (no PIN needed)
 LOCATION:https://www.uberconference.com/opencontainers