readme: update installation link for pvlib#1173

Author: kandersolar

README.md

@@ -108,7 +108,7 @@ Installation
 ============
 
 pvlib-python releases may be installed using the ``pip`` and ``conda`` tools.
-Please see the [Installation page](http://pvlib-python.readthedocs.io/en/stable/installation.html) of the documentation for complete instructions.
+Please see the [Installation page](https://pvlib-python.readthedocs.io/en/stable/user_guide/installation.html) of the documentation for complete instructions.
 
 
 Contributing