Update to GitHib repo path and addition of Slack coordinates
Update to GitHib repo path and addition of Slack coordinates

OpenAstronomy/openastronomy.github.io,Cadair/openastronomy.github.io,dpshelio/openastronomy.github.io,Cadair/openastronomy.github.io,dpshelio/openastronomy.github.io,dpshelio/openastronomy.github.io,OpenAstronomy/openastronomy.github.io,OpenAstronomy/openastronomy.github.io,Cadair/openastronomy.github.io