init/clone: remove short option -L and document --separate-git-dir

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-clone.txt b/Documentation/git-clone.txt
index 86eb4c9..b093e45 100644
--- a/Documentation/git-clone.txt
+++ b/Documentation/git-clone.txt
@@ -12,7 +12,7 @@
 'git clone' [--template=<template_directory>]
 	  [-l] [-s] [--no-hardlinks] [-q] [-n] [--bare] [--mirror]
 	  [-o <name>] [-b <name>] [-u <upload-pack>] [--reference <repository>]
-	  [--separate-git-dir|-L <git dir>]
+	  [--separate-git-dir <git dir>]
 	  [--depth <depth>] [--recursive|--recurse-submodules] [--] <repository>
 	  [<directory>]
 
@@ -177,7 +177,6 @@
 	repository does not have a worktree/checkout (i.e. if any of
 	`--no-checkout`/`-n`, `--bare`, or `--mirror` is given)
 
--L=<git dir>::
 --separate-git-dir=<git dir>::
 	Instead of placing the cloned repository where it is supposed
 	to be, place the cloned repository at the specified directory,