Add docs for releasing plus test of entry points

[znicholls]

Pull request

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Example added (either to an existing notebook or as a new notebook, where applicable) (N/A)
• 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 <https://github.com/znicholls/silicone/pull/XX>`_) Added feature which does something
- (`#XX <https://github.com/znicholls/silicone/pull/XX>`_) Fixed bug identified in (`#YY <https://github.com/znicholls/silicone/issues/YY>`_)

[codecov]

Codecov Report

Merging #19 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #19   +/-   ##
=======================================
  Coverage   95.22%   95.22%           
=======================================
  Files           9        9           
  Lines         314      314           
  Branches       52       52           
=======================================
  Hits          299      299           
  Misses         11       11           
  Partials        4        4

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