docs: add request body format to public API definition

The request body format has always been part of the public API.

This adds it to the documentation of the public API.

README.md

@@ -103,8 +103,8 @@ This project is versioned using [Semantic Versioning 2.0.0](https://semver.org/s
 
 The public API is defined as:
 
-- The API endpoints, meaning the routes, parameters, HTTP respone codes and response body format (for a function, we'd just say “the function signature“) that the HTTP server built from the code in this repository provides
-- The behavior of the API endpoints no matter the signature of the endpoint is
+- The API endpoints, meaning the routes, parameters, HTTP response codes, and request and response body format 
+- The behavior of the API endpoints no matter the signature of the endpoint is.
 
 Not part of the public API is: