message: remove the word usage in readme
diff: @@ -7,7 +7,7 @@ Tests are ran against our own test vectors in `tests/test_vectors`.
  You can re-generate the test vectors by using:
  ```text
  -usage: cargo run -p export_test_vectors -- [Hex|B10] [legacy|kimchi] <OUTPUT_FILE>
  +cargo run -p export_test_vectors -- [Hex|B10] [legacy|kimchi] <OUTPUT_FILE>
  ```
  Examples
  