[PATCH] Improve --assume-unchanged in the git update-index man page

Hi Junio, this is my quick attempt at a patch for the man page.

In $gmane/260837 the --assume-unchanged flag was reported as buggy because of a misunderstanding about what it is being promised.

This patch looks to be more assertive in stating what promise is being made.

While at it correct a confusing pluralisation of the option.

Philip Oakley (1):
  doc: make clear --assume-unchanged's user contract

 Documentation/git-update-index.txt | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)