Add important usage notice to README

[broven]

Added important notice regarding the use of the proxy and its compliance with Anthropic's Terms of Service.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.64%. Comparing base (7a4b5e4) to head (6ac9a47).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #30   +/-   ##
=======================================
  Coverage   85.64%   85.64%           
=======================================
  Files          15       15           
  Lines        1198     1198           
  Branches      358      353    -5     
=======================================
  Hits         1026     1026           
  Misses        171      171           
  Partials        1        1           

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