ngtip: make revset help text slightly more descriptive

8 jobs for topic/default/issue6405-ngtip-typerror in 4 minutes and 3 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #112066
checks-py2

00:02:01

passed #112067
checks-py3

00:02:10

passed #112072
doc

00:00:19

manual #112065
allowed to fail manual
pytype
passed #112068
tests-py2-cext

00:04:02

passed #112069
tests-py2-pure

00:02:28

passed #112070
tests-py3-cext

00:04:03

passed #112071
tests-py3-pure

00:03:14