Add notes and contribution info to readme

[c24t]

Add a stub readme with a link to the SIG meeting notes to fix #13.

[Oberon00]

I can't find a link to the meeting itself (hangout): Neither here, nor in the community README, nor in the linked Google calendar.

Also I'm not sure we should duplicate the information from the community README. IMHO, only one of the two READMEs should document the specifics and there should be a link to the one that does in the other.

On another note, reading "At least 1 approving review is required by reviewers with write access. ", I don't think I have write access: I'm in the OpenTelemetry org, but not in any teams.

[c24t]

I can't find a link to the meeting itself (hangout)

The hangout info is in the calendar event details:

Joining info | meet.google.com/yyw-hqif-wmu
Or dial: +1 601-658-0516  PIN: 736063

but it sounds like we should switch this to zoom in any case. @carlosalberto do you have a link we can use while we're waiting for the CNCF zoom? I'll update the calendar event to include it.

only one of the two READMEs should document the specifics and there should be a link to the one that does in the other

I agree with that in principle, but I was trying to make it as easy as possible for people just browsing the repo.

I don't think I have write access

I looks like I don't have admin access to give you write access... I'll follow up in person.