doc: normalize [--options] to [options] in git-diff

SYNOPSIS and other manuals use [options] but DESCRIPTION
used [--options].

Signed-off-by: Andreas Heiduk <asheiduk@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: asheiduk

Documentation/git-diff.txt

@@ -21,15 +21,15 @@ Show changes between the working tree and the index or a tree, changes
 between the index and a tree, changes between two trees, changes between
 two blob objects, or changes between two files on disk.
 
-'git diff' [--options] [--] [<path>...]::
+'git diff' [options] [--] [<path>...]::
 
 	This form is to view the changes you made relative to
 	the index (staging area for the next commit).  In other
 	words, the differences are what you _could_ tell Git to
 	further add to the index but you still haven't.  You can
 	stage these changes by using linkgit:git-add[1].
 
-'git diff' [--options] --no-index [--] <path> <path>::
+'git diff' [options] --no-index [--] <path> <path>::
 
 	This form is to compare the given two paths on the
 	filesystem.  You can omit the `--no-index` option when
@@ -38,7 +38,7 @@ two blob objects, or changes between two files on disk.
 	or when running the command outside a working tree
 	controlled by Git.
 
-'git diff' [--options] --cached [<commit>] [--] [<path>...]::
+'git diff' [options] --cached [<commit>] [--] [<path>...]::
 
 	This form is to view the changes you staged for the next
 	commit relative to the named <commit>.  Typically you
@@ -48,26 +48,26 @@ two blob objects, or changes between two files on disk.
 	<commit> is not given, it shows all staged changes.
 	--staged is a synonym of --cached.
 
-'git diff' [--options] <commit> [--] [<path>...]::
+'git diff' [options] <commit> [--] [<path>...]::
 
 	This form is to view the changes you have in your
 	working tree relative to the named <commit>.  You can
 	use HEAD to compare it with the latest commit, or a
 	branch name to compare with the tip of a different
 	branch.
 
-'git diff' [--options] <commit> <commit> [--] [<path>...]::
+'git diff' [options] <commit> <commit> [--] [<path>...]::
 
 	This is to view the changes between two arbitrary
 	<commit>.
 
-'git diff' [--options] <commit>..<commit> [--] [<path>...]::
+'git diff' [options] <commit>..<commit> [--] [<path>...]::
 
 	This is synonymous to the previous form.  If <commit> on
 	one side is omitted, it will have the same effect as
 	using HEAD instead.
 
-'git diff' [--options] <commit>\...<commit> [--] [<path>...]::
+'git diff' [options] <commit>\...<commit> [--] [<path>...]::
 
 	This form is to view the changes on the branch containing
 	and up to the second <commit>, starting at a common ancestor