add forum link(s)

[dkebler]

please put a forum link next to the blog link in upper right navbar.
Might put it in page footer section as well next to 'contact'
Until I was told I had no idea you all have a forum server.

[bjorn]

There is a forum? I definitely agree a link would be useful...

Would also have been nice to link it from this issue. ;-)

[luceos]

https://forum.opencollective.com

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