Fix typo in usage.md

[morenoh149]

No description provided.

[codecov-io]

Codecov Report

Merging #379 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #379   +/-   ##
========================================
  Coverage    93.05%   93.05%           
========================================
  Files           51       51           
  Lines         2665     2665           
========================================
  Hits          2480     2480           
  Misses         185      185

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[mblayman]

Thanks! 👍