Document a couple of missing command-line options.

This patch adds documentation to quite a few command-line options.

Signed-off-by: Nikolai Weibull <nikolai@bitwi.se>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-checkout-index.txt

@@ -18,21 +18,21 @@ Will copy all files listed from the index to the working directory
 
 OPTIONS
 -------
--u::
+-u|--index::
 	update stat information for the checked out entries in
 	the index file.
 
--q::
+-q|--quiet::
 	be quiet if files exist or are not in the index
 
--f::
+-f|--force::
 	forces overwrite of existing files
 
--a::
+-a|--all::
 	checks out all files in the index.  Cannot be used
 	together with explicit filenames.
 
--n::
+-n|--no-create::
 	Don't checkout new files, only refresh files already checked
 	out.
 

Documentation/git-prune-packed.txt

@@ -23,6 +23,12 @@ compression applied, stored in a single file, with an associated index file.
 
 Packs are used to reduce the load on mirror systems, backup engines, disk storage, etc.
 
+OPTIONS
+-------
+-n::
+        Don't actually remove any objects, only show those that would have been
+        removed.
+
 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>

Documentation/git-read-tree.txt

@@ -30,6 +30,10 @@ OPTIONS
 -m::
 	Perform a merge, not just a read.
 
+--reset::
+
+        Same as -m except that unmerged entries will be silently ignored.
+
 -u::
 	After a successful merge, update the files in the work
 	tree with the result of the merge.