📝 Add user guide file to docs

[dalonsoa]

Description

Adds the existing user_guide.md file to the MkDocs documentation, so it is rendered alongside everything else. This file is just a placeholder. Populating the guide will be done in #350 .

Fixes #346

Type of change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Documentation (non-breaking change that adds or improves the documentation)
• Optimisation (non-breaking, back-end change that speeds up the code)

Key checklist

• Pre-commit hooks run successfully (pre-commit run -a)
• All tests pass (pytest)
• The documentation builds without warnings (mkdocs build -s)
• Check the GUI still works (if relevant)
• Check the code works with actual hardware (if relevant)
• Check the pyinstaller-built executable works (if relevant)

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests have been added or an issue has been opened to tackle that in the future. (Indicate issue here: # (issue))

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.99%. Comparing base (f014b51) to head (550c79f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #679   +/-   ##
=======================================
  Coverage   84.99%   84.99%           
=======================================
  Files          69       69           
  Lines        3459     3459           
=======================================
  Hits         2940     2940           
  Misses        519      519           

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[alexdewar]

LGTM!