add: document the chmod option

The git add --chmod option was introduced in 4e55ed3 ("add: add
--chmod=+x / --chmod=-x options", 2016-05-31), but was never
documented.  Document the feature.

Signed-off-by: Thomas Gummerer <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: tgummerer

Documentation/git-add.txt

@@ -11,7 +11,7 @@ SYNOPSIS
 'git add' [--verbose | -v] [--dry-run | -n] [--force | -f] [--interactive | -i] [--patch | -p]
 	  [--edit | -e] [--[no-]all | --[no-]ignore-removal | [--update | -u]]
 	  [--intent-to-add | -N] [--refresh] [--ignore-errors] [--ignore-missing]
-	  [--] [<pathspec>...]
+	  [--chmod=(+|-)x] [--] [<pathspec>...]
 
 DESCRIPTION
 -----------
@@ -165,6 +165,11 @@ for "git add --no-all <pathspec>...", i.e. ignored removed files.
 	be ignored, no matter if they are already present in the work
 	tree or not.
 
+--chmod=(+|-)x::
+	Override the executable bit of the added files.  The executable
+	bit is only changed in the index, the files on disk are left
+	unchanged.
+
 \--::
 	This option can be used to separate command-line options from
 	the list of files, (useful when filenames might be mistaken