Add read the docs yml and remove requirements

[znicholls]

Pull request

Please confirm that this pull request has done the following:

• [x] Tests added
• [x] Documentation added (where applicable)
• [x] Example added (either to an existing notebook or as a new notebook, where applicable)
• [x] Description in CHANGELOG.rst added

Adding to CHANGELOG.rst

Please add a single line in the changelog notes similar to one of the following:

- (`#XX <http://link-to-pr.com>`_) Added feature which does something
- (`#XX <http://link-to-pr.com>`_) Fixed bug identified in (`#XX <http://link-to-issue.com>`_)

@chrisroadmap is it possible for you to see if this branch builds on read the docs?

[codecov[bot]]

Codecov Report

Merging #47 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #47   +/-   ##
=======================================
  Coverage   90.47%   90.47%           
=======================================
  Files          33       33           
  Lines        1260     1260           
=======================================
  Hits         1140     1140           
  Misses        120      120

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