Meetings should have an anouncement field

[YoBoY]

When we add a meeting we can't add a link to the website where all the information regardings the meeting are like :
- how to participate
- agenda
- where to talk about the meeting and the agenda items
- where to find documents, charts, etc for the preparation of the meeting.

Like the events, it is necessary to have a link also to point where the loco team holds the informations.

[Chris Johnston (cjohnston)]

As mentioned on IRC...

How to participate: there is a channel listed on the page, and if it isn't already released, soon a link to join the channel from LD.
Agenda: That's a feature of the meetings part of LD
Where to talk about the meeting and the agenda items: Well.. the channel listed works if it isn't #ubuntu-meetings, otherwise the default team channel or team ML work.
Where to find docs, charts, etc: these should be listed in the description section of agenda items.