suggestion of T. Kloss: make installation from source easier to find

content/install.rst

@@ -31,13 +31,14 @@ The instructions below assume Python 3.  They should be also valid for Python
 ``python``, ``pip``.
 
 
-Choose your platform
-====================
+Platforms
+=========
 Installation instructions are available for the major operating systems:
 
 + `GNU/Linux`_
 + `Mac OS X`_
 + `Microsoft Windows`_
++ `Building from source`_
 
 GNU/Linux
 =========