docs(readme): spelling fixes (#560)

Author: Fdawgs

README.md

@@ -650,13 +650,13 @@ AJV Serialize large array x 58.76 ops/sec ±4.59% (60 runs sampled)
 Treat the schema definition as application code, it
 is not safe to use user-provided schemas.
 
-In order to achieve lowest cost/highest performance redaction `fast-json-stringify`
+To achieve low cost and high performance redaction `fast-json-stringify`
 creates and compiles a function (using the `Function` constructor) on initialization.
 While the `schema` is currently validated for any developer errors,
 there is no guarantee that supplying user-generated schema could not
 expose your application to remote attacks.
 
-Users are responsibile for sending trusted data. `fast-json-stringify` guarantees that you will get
+Users are responsible for sending trusted data. `fast-json-stringify` guarantees that you will get
 a valid output only if your input matches the schema or can be coerced to the schema. If your input
 doesn't match the schema, you will get undefined behavior.