Slack page info refresh + slack info channel

[chris-tse]

We'd like to revamp the info on the /slack page. Some of the screenshots are outdated and the instructions could be more straightforward. The suggested channel list should also be more clear in what topics should be discussed where.

#freecodecamp -> #code-newbies

[kacollins]

Is anyone working on this? If not, @JakeFellwock would you like to?

[JakeFellwock]

Yes, Ill work on this one. Thanks!