"lessc" task (and 4 others) is (are) not documented

[allentiak]

When comparing the built-ins Guide against https://github.com/hashobject/perun/blob/master/src/io/perun.clj, there are five tasks that aren't even mentioned (I haven't checked their names yet, though -- only compared the amount of times deftask is mentioned in the code).

In the case of lessc, one cannot even know which version should be used (the Python one?, the Node.js one?)...

@podviaznikov Could you please write a short comment on the functionality of this task? If it's too much of a burden, I could copy it to the guide myself...