Update README.md

Fix install commands and broken installation link in README

Author: brwerx

README.md

@@ -74,6 +74,10 @@ Installation
 ============
 
 pvlib-python releases may be installed using the ``pip`` and ``conda`` tools.
+```bash
+pip install pvlib
+conda install -c conda-forge pvlib
+```
 Please see the [Installation page](https://pvlib-python.readthedocs.io/en/stable/user_guide/getting_started/installation.html) of the documentation for complete instructions.