update: do not use the term 'update' when mentioning reverting one file
and give a more precise hint for how to revert such a file
I'm using the term 'revision' instead of 'changeset' in this change to be
consistent with the REV we use in the synopsis.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a