Add Pub badge

[creativecreatorormaybenot]

This has three major benefits:

• Showing that the package is on Pub.
• Showing what version is currently published.
• Allowing to go there by click.

[codecov-commenter]

Codecov Report

Merging #5 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #5   +/-   ##
=======================================
  Coverage   74.62%   74.62%           
=======================================
  Files          99       99           
  Lines        4689     4689           
=======================================
  Hits         3499     3499           
  Misses       1190     1190           

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[znjameswu]

Thank you for your contribution!