Update README.md

[obackhouse]

Adds section on backends and precision

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.59%. Comparing base (45372fc) to head (3ad5335).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #101   +/-   ##
=======================================
  Coverage   89.59%   89.59%           
=======================================
  Files         111      111           
  Lines      116199   116199           
  Branches      781      781           
=======================================
  Hits       104106   104106           
  Misses      11851    11851           
  Partials      242      242           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.