Merge pull request #2203 from Lukasa/remove_certifi

Remove hard certifi dependency and document.

diff --cc docs/user/advanced.rst
Simple merge

diff --cc setup.py
index c89f8f9fa6d45c6a1ef0b56248d09ea9a04436c2,b790ec71ab0c193360a7e250f0c05a2b61934960..813fc87979759f76b12b2c6fd34faffc32ea4dd3
--- 1/setup.py
--- 2/setup.py
+++ b/setup.py
@@@ -27,11 -25,11 +27,11 @@@ packages = 
      'requests.packages.urllib3.packages.ssl_match_hostname',
  ]
  
- requires = ['certifi']
+ requires = []
  
 -with open('README.rst') as f:
 +with open('README.rst', 'r', 'utf-8') as f:
      readme = f.read()
 -with open('HISTORY.rst') as f:
 +with open('HISTORY.rst', 'r', 'utf-8') as f:
      history = f.read()
  
  setup(