Make README.txt consistent reStructuredText

It seems that the README file is formatted as reStructuredText, but not
consistently.

README.txt → README.rst

@@ -1,17 +1,18 @@
+##########
 matplotlib
-==========
+##########
 
 matplotlib is a python 2D plotting library which produces publication
 quality figures in a variety of hardcopy formats and interactive
 environments across platforms. matplotlib can be used in python
 scripts, the python and ipython shell (ala matlab or mathematica), web
 application servers, and various graphical user interface toolkits.
 
-Home page: <http://matplotlib.org/>
-
+`Home page <http://matplotlib.org/>`_
 
 Installation
 =============
+
 For installation instructions and requirements, see the INSTALL file.
 
 Testing