Documentation/git-cherry-pick.txt et al.: Fix misleading -n description

Documentation/git-cherry-pick.txt et al.: Fix misleading -n description

The manual page of git-cherry-pick and git-revert asserts that -n works
primarily on the working tree, while in fact the primary object it operates
on is the index, and the changes only "accidentally" propagate to the
working tree. This e.g. leads innocent #git IRC folks to believe that you
can use -n to prepare changes for git-add -i staging.

Signed-off-by: Petr Baudis <redacted>
Signed-off-by: Junio C Hamano <redacted>