docs: fix typo in readme

[tanmen]

I felt this was a misspelling, but I didn't understand.
If you misspell and find this fix useful, please incorporate my fix if you like.

I didn't create an issue because it's a small change.

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[codecov]

Codecov Report

Merging #1331 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1331   +/-   ##
=======================================
  Coverage   99.00%   99.00%           
=======================================
  Files          14       14           
  Lines       11719    11719           
  Branches      582      513   -69     
=======================================
  Hits        11602    11602           
  Misses        117      117           

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[tanmen]

I just signed the cla.

[tanmen]

@JustinBeckwith Thank you for review and marge X)
I so happy :)