Point documentation to http: instead of https:

The certificate at that URL is for `readthedocs.io`, so if you want to use https, it's best to use `flake8.readthedocs.io` and not `flake8.pycqa.org`.  As it is currently, you get a certificate error.

Note also that the `Code of Conduct` and `Getting Started Contributing` links are using `http` and pointing to the insecure domain, so if you do want https, you should change those as well.

README.rst

@@ -53,7 +53,7 @@ to suggest, the mailing list would be the best place for it.
 Links
 =====
 
-* `Flake8 Documentation <https://flake8.pycqa.org/en/latest/>`_
+* `Flake8 Documentation <http://flake8.pycqa.org/en/latest/>`_
 
 * `GitLab Project <https://gitlab.com/pycqa/flake8>`_