git-gui: Change summary of git-gui.

Since git-gui does more than create commits, it is unfair to call
it "a commit creation tool".  Instead lets just call it a graphical
user interface.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-gui.sh

@@ -4559,7 +4559,7 @@ proc do_about {} {
 	pack $w.buttons -side bottom -fill x -pady 10 -padx 10
 
 	label $w.desc \
-		-text "git-gui - a commit creation tool for Git.
+		-text "git-gui - a graphical user interface for Git.
 $copyright" \
 		-padx 5 -pady 5 \
 		-justify left \