doc: Change link in README to external link.

Changed the link to the ReST documentation to a external link for reusability.

Change-Id: Ia575717c0fb92672828bb11854c9a8a1268af464
Signed-off-by: Rodrigo Caballero <rodrigo.caballero.abraham@intel.com>
diff --git a/doc/README.rst b/doc/README.rst
index e23b016..1a20b2a 100644
--- a/doc/README.rst
+++ b/doc/README.rst
@@ -2,8 +2,8 @@
 ########################
 
 .. This document is in Restructured Text Format.
-
-   More information at `<http://sphinx-doc.org/rest.html>`_.
+   Find more information regarding the ReST markup in the
+   `ReST documentation`_.
    This is a comment that won't show up in formatted output
 
 Welcome to the Zephyr Project.
@@ -11,7 +11,6 @@
 Thank you for your interest in the Zephyr Project. These instructions are
 designed to walk you through generating the Zephyr Project's documentation.
 
-
 Documentation Notes
 *******************
 
@@ -49,7 +48,7 @@
    Make sure that ``Doxygen`` is installed in your system.
    The installation of Doxygen is beyond the scope of this document.
 
-Running the documentation generators
+Running the Documentation Generators
 ************************************
 
 Assuming that the Zephyr Project tree with the doc directory is in
@@ -71,3 +70,5 @@
 
 If you want the LaTeX PDF output, you need to install all the Latex
 packages first. That installation is beyond the scope of this document.
+
+.. _ReST documentation: http://sphinx-doc.org/rest.html
\ No newline at end of file