improve prominence of bazel build guidance for iOS targets

[hborawski]

match the note style in the later part of the doc with newer markdown features in github, should make this section more clear

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.57%. Comparing base (fb57765) to head (e662b21).
Report is 28 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #546   +/-   ##
=======================================
  Coverage   89.57%   89.57%           
=======================================
  Files         331      331           
  Lines       19718    19718           
  Branches     1949     1949           
=======================================
  Hits        17663    17663           
  Misses       2041     2041           
  Partials       14       14           

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