I think it would be fun to have an IRC channel (that shows as another tab in the CodinGame chat pane) that broadcasts as people earn achievements. That way people can see and congratulate when people they know online achieve something difficult, or congratulate new players on finishing their first puzzles.
If achievements are earned often enough that it would flood the channel, perhaps filter to achievements worth over a certain number of points, or filter out achievements that are not related to puzzle completion.
The announcements could look something like:
Porthos3 has earned the achievement Babylon Tower (50 CP)!
The announcements could even potentially be color coded based upon type of achievement or the number of CP earned.