docs: new banner

[thymikee]

Summary

We're adding new banners to Callstack repos :)

Test plan

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.38%. Comparing base (3fe3b76) to head (a2b791f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1775   +/-   ##
=======================================
  Coverage   95.38%   95.38%           
=======================================
  Files          94       94           
  Lines        5245     5245           
  Branches      892      892           
=======================================
  Hits         5003     5003           
  Misses        242      242           

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