Add timeanddate.com url that points to the meeting time to e-mail

It's daylight saving time season, easier this way than to having to remember to announce every time there's a DST change.

Example Output:
```
demosdemon@Marry-Anne:~/Projects/gits/statler-waldorf$ ./announce.py
Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Subject: Dev chat reminder, issue a6393a7b-8463-4442-ae9c-8be206351da4
From: Statler & Waldorf <noreply@musicbrainz.org>
To: MusicBrainz Developer Discussion <musicbrainz-devel@lists.musicbrainz.org>
Message-ID: <meeting-announcement-a6393a7b-8463-4442-ae9c-8be206351da4@musicbrainz.org>

We've got our weekly dev chat on 2013-03-11 on IRC in #musicbrainz-devel on irc.freenode.net. We're going to meet at Regular Meeting Time [1] (20:00 UTC) [2].

If there is any topic you would like to discuss during the meeting, please add it to the agenda in the channel topic.

[1] http://musicbrainz.org/doc/Development_Chat
[2] http://www.timeanddate.com/worldclock/fixedtime.html?iso=20130311T20

--
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```