Documentation: git-init: --separate-git-dir: clarify

Use shorter sentences to describe what actually happens. We describe
what the term "Git symbolic link" actually means.

Also, we separate out the description of the behavioral change upon
reinitialization into its own paragraph.

Signed-off-by: Linus Arver <linusarver@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-init.txt

@@ -57,12 +57,12 @@ DIRECTORY" section below.)
 
 --separate-git-dir=<git dir>::
 
-Instead of initializing the repository where it is supposed to be,
-place a filesytem-agnostic Git symbolic link there, pointing to the
-specified path, and initialize a Git repository at the path. The
-result is Git repository can be separated from working tree. If this
-is reinitialization, the repository will be moved to the specified
-path.
+Instead of initializing the repository as a directory to either `$GIT_DIR` or
+`./.git/`, create a text file there containing the path to the actual
+repository.  This file acts as filesystem-agnostic Git symbolic link to the
+repository.
++
+If this is reinitialization, the repository will be moved to the specified path.
 
 --shared[=(false|true|umask|group|all|world|everybody|0xxx)]::