git-cat-file.txt: Document --textconv

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-cat-file.txt

@@ -9,14 +9,15 @@ git-cat-file - Provide content or type and size information for repository objec
 SYNOPSIS
 --------
 [verse]
-'git cat-file' (-t | -s | -e | -p | <type>) <object>
+'git cat-file' (-t | -s | -e | -p | <type> | --textconv ) <object>
 'git cat-file' (--batch | --batch-check) < <list-of-objects>
 
 DESCRIPTION
 -----------
 In its first form, the command provides the content or the type of an object in
 the repository. The type is required unless '-t' or '-p' is used to find the
-object type, or '-s' is used to find the object size.
+object type, or '-s' is used to find the object size, or '--textconv' is used
+(which implies type "blob").
 
 In the second form, a list of objects (separated by linefeeds) is provided on
 stdin, and the SHA1, type, and size of each object is printed on stdout.
@@ -51,6 +52,11 @@ OPTIONS
 	or to ask for a "blob" with <object> being a tag object that
 	points at it.
 
+--textconv::
+	Show the content as transformed by a textconv filter. In this case,
+	<object> has be of the form <treeish>:<path>, or :<path> in order
+	to apply the filter to the content recorded in the index at <path>.
+
 --batch::
 	Print the SHA1, type, size, and contents of each object provided on
 	stdin. May not be combined with any other options or arguments.