Change discussion post text in worksheets

[kolkhis]

Links to discussion posts are pointing towards #prolug-projects threads. With the new forum board, the links to that channel should be changed to reflect the new location.

The forum just started for unit 5 of the second round. The older discussion posts are still in #prolug-projects, so we should talk about what to do about this during our next meeting.

[kolkhis]

This will need to be fixed on the next round of the course. Before unit 5, all discussion posts are still in the #prolug-projects channel, on the next round they should all be in the forum channel.

We'll leave this up and take care of that once we're on the next round.