Add docs about how to use docker for when autogen itself is run in docker

[jackgerrits]

Why are these changes needed?

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 36.79%. Comparing base (8f6590e) to head (b03edf4).
Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2052      +/-   ##
==========================================
- Coverage   37.55%   36.79%   -0.76%     
==========================================
  Files          65       66       +1     
  Lines        6910     7060     +150     
  Branches     1520     1541      +21     
==========================================
+ Hits         2595     2598       +3     
- Misses       4090     4234     +144     
- Partials      225      228       +3     

Flag	Coverage Δ
unittests	36.79% <ø> (-0.76%)	⬇️

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