initial doc for xlang

[rysweet]

Why are these changes needed?

adds some docs for clang and .NET

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.

[Copilot]

Copilot reviewed 1 out of 1 changed files in this pull request and generated 4 comments.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.35%. Comparing base (20245b1) to head (f308201).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5476   +/-   ##
=======================================
  Coverage   78.35%   78.35%           
=======================================
  Files         167      167           
  Lines        9926     9926           
=======================================
  Hits         7778     7778           
  Misses       2148     2148           

Flag	Coverage Δ
unittests	78.35% <ø> (ø)

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