manpages: italicize gitk's name (where it was in teletype font) The name `gitk` is sometimes meant to be entered at the command prompt, but most uses are just referring to the program with that name (not the incantation to start it). Signed-off-by: Jonathan Nieder <jrnieder@uchicago.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>