Update issue creation link in README

[jonathan343]

This PR updates the botocore README to point to https://github.com/boto/botocore/issues/new/choose which allows users to create a new issue using custom templates instead of the basic https://github.com/boto/botocore/issues/new

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2c790d2) 93.14% compared to head (f7f4d01) 93.14%.
Report is 3 commits behind head on develop.

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Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3103   +/-   ##
========================================
  Coverage    93.14%   93.14%           
========================================
  Files           66       66           
  Lines        14237    14237           
========================================
  Hits         13261    13261           
  Misses         976      976           

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