add info about the Slack channel

[cholmes]

There's now a slack for COG's. We should add that to the site so people know about it.

[cholmes]

URL to join slack is: https://cogeotiff.slack.com/join/shared_invite/zt-i37rlzlz-L0KYH3SWsIwzM~dbBbjM1w#/

[cholmes]

And a short version: http://bit.ly/cog_slack

[terezapohankova]

Does the channel still work? Anytime I try to launch it, it never shows anything

[vincentsarago]

you can try this link: https://join.slack.com/t/cogeotiff/shared_invite/zt-17by75auf-39YWJEM08MkwEyM67TqeDg

[NathanPB]

It says "Please contact your orgs owner to resent it"

[nikkopante]

Hi. I think its not available for the public.

[batugane]

Added Slack icon to the footer with hover effects. Included in my latest pull request #66.