Contributing link on Readme is broken

[matsuobasho]

Describe the bug
Link to the contributing page on Readme is broken
http://pvlib-python.readthedocs.io/en/stable/contributing.html

To Reproduce
Steps to reproduce the behavior:

1. Go to Readme
2. Click on 'Contributing page'
3. See error

Expected behavior
Contributing page.

[mikofski]

Hi @matsuobasho to whom should I give credit in contributors?