ngtip: make revset help text slightly more descriptive

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branch : stable
7 jobs for topic/stable/issue6405-ngtip-typerror in 5 minutes and 25 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed doc #113751

00:00:39

passed flake8 #113745

00:00:36

manual pytype #113746
allowed to fail manual
passed tests-py2-cext #113747

00:03:59

passed tests-py2-pure #113748

00:03:22

passed tests-py3-cext #113749

00:05:25

passed tests-py3-pure #113750

00:03:26