Add badges in `README` for integration tests and code coverage

[m-Peter]

This will add two badges in the README, as shown below:

[codecov-commenter]

Codecov Report

Merging #150 (d7ffa26) into main (983cba8) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #150   +/-   ##
=======================================
  Coverage   82.50%   82.50%           
=======================================
  Files           4        4           
  Lines         343      343           
=======================================
  Hits          283      283           
  Misses         60       60