docs(core_distributed-group-chat): fix the typos in the docs in the README.md

[jsburckhardt]

Why are these changes needed?

Wrong file names in the README.md

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]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.02%. Comparing base (b89ca2a) to head (0511771).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5347   +/-   ##
=======================================
  Coverage   76.02%   76.02%           
=======================================
  Files         157      157           
  Lines        9491     9491           
=======================================
  Hits         7216     7216           
  Misses       2275     2275           

Flag	Coverage Δ
unittests	76.02% <ø> (ø)

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[MohMaz]

Thanks for the PR and the fix!