update runtime docs, thanks @uniphil!

#117

Readme.md

@@ -35,9 +35,9 @@ You can also add it to upcoming builds of an existing application:
 
     $ heroku config:add BUILDPACK_URL=git://github.com/heroku/heroku-buildpack-python.git
 
-The buildpack will detect your app as Python if it has the file `requirements.txt` in the root. 
+The buildpack will detect your app as Python if it has the file `requirements.txt` in the root.
 
-It will use Pip to install your dependencies, vendoring a copy of the Python runtime into your slug. 
+It will use Pip to install your dependencies, vendoring a copy of the Python runtime into your slug.
 
 Specify a Runtime
 -----------------
@@ -45,10 +45,12 @@ Specify a Runtime
 You can also provide arbitrary releases Python with a `runtime.txt` file.
 
     $ cat runtime.txt
-    python-3.3.2
-    
+    python-3.3.3
+
 Runtime options include:
 
-- python-2.7.4
-- python-3.3.2
+- python-2.7.6
+- python-3.3.4
 - pypy-1.9 (experimental)
+
+Other [unsupported runtimes](https://github.com/kennethreitz/python-versions/tree/master/formula) are available as well.