Backport commit 9bff405d0 from Emacs

* doc/org.texi (Installation): Fix clone commands.

9bff405d09f6eeeb577e6e0111e49f35d3b95b52
Michael Albinus
Wed Mar 28 10:38:26 2018 +0200

doc/org.texi

@@ -923,6 +923,7 @@ You can clone Org's repository and install Org like this:
 @example
 $ cd ~/src/
 $ git clone https://code.orgmode.org/bzg/org-mode.git
+$ cd org-mode/
 $ make autoloads
 @end example