Document log levels in help

After having to figure out this in source code, I think it's better to document this in help.
6 jobs for patch-1 in 2 minutes and 45 seconds (queued for 5 seconds)
latest
Status Job ID Name Coverage
  Test
passed #251800
cppcheck

00:00:29

passed #251801
luacheck

00:00:29

passed #251798
system-tests

00:01:22

passed #251799
system-valgrind-tests

00:02:45

passed #251796
unit-tests

00:00:52

passed #251797
unit-valgrind-tests

00:02:11