doc: update readme #161

[hayleyling]

1. Correct some minor errors in the readme file.
2. Add icons to make it more readable.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68%. Comparing base (21c30dd) to head (0abafff).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff          @@
##           master   #162   +/-   ##
=====================================
- Coverage      69%    68%   -1%     
=====================================
  Files          51     51           
  Lines        4601   4601           
=====================================
- Hits         3175   3170    -5     
- Misses       1173   1177    +4     
- Partials      253    254    +1     

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