Add docstring to synchrotron class

[Villtord]

Add docstring to synchrotron class.

Instructions to reviewer on how to test:

1. Do thing x
2. Confirm thing y happens

Checks for reviewer

• Would the PR title make sense to a scientist on a set of release notes
• If a new device has been added does it follow the standards
• If changing the API for a pre-existing device, ensure that any beamlines using this device have updated their Bluesky plans accordingly
• Have the connection tests for the relevant beamline(s) been run via dodal connect ${BEAMLINE}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.09%. Comparing base (c340ca5) to head (4d4f1cc).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1877   +/-   ##
=======================================
  Coverage   99.09%   99.09%           
=======================================
  Files         303      303           
  Lines       11446    11446           
=======================================
  Hits        11342    11342           
  Misses        104      104           

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