Add section on quantum noise to user guide

[Misty-W]

Description

Add links to resources on quantum noise (from IBM Qiskit Global Summer School) to ""About Error Mitigation" section of user guide. See Discord conversation for context.

License

• I license this contribution under the terms of the GNU GPL, version 3 and grant Unitary Fund the right to provide additional permissions as described in section 7 of the GNU GPL, version 3.

Before opening the PR, please ensure you have completed the following where appropriate.

• I added unit tests for new code.
• I used type hints in function signatures.
• I used Google-style docstrings for functions.
• I updated the documentation where relevant.
• Added myself / the copyright holder to the AUTHORS file

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (b6cb5c1) 98.28% compared to head (5519655) 98.28%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2036   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files          86       86           
  Lines        4084     4084           
=======================================
  Hits         4014     4014           
  Misses         70       70           

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