git-add --all: documentation

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-add.txt

@@ -9,7 +9,7 @@ SYNOPSIS
 --------
 [verse]
 'git add' [-n] [-v] [--force | -f] [--interactive | -i] [--patch | -p]
-	  [--update | -u] [--refresh] [--ignore-errors] [--]
+	  [--all | [--update | -u]] [--refresh] [--ignore-errors] [--]
 	  <filepattern>...
 
 DESCRIPTION
@@ -86,6 +86,12 @@ OPTIONS
 	command line. If no paths are specified, all tracked files in the
 	current directory and its subdirectories are updated.
 
+-A::
+--all::
+	Update files that git already knows about (same as '\--update')
+	and add all untracked files that are not ignored by '.gitignore'
+	mechanism.
+
 --refresh::
 	Don't add the file(s), but only refresh their stat()
 	information in the index.