Explicitly set sphinx config path for readthedocs (fixes #115)

[RalfG]

Fixed

• Docs: Explicitly set sphinx config path for readthedocs (fixes Read the Docs Link Unavailable #115)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.12%. Comparing base (45bc0b6) to head (4152964).
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #118   +/-   ##
=======================================
  Coverage   69.12%   69.12%           
=======================================
  Files          30       30           
  Lines        2792     2792           
=======================================
  Hits         1930     1930           
  Misses        862      862           

Flag	Coverage Δ
unittests	69.12% <ø> (ø)

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