No mention of Content-Type application/graphql in the README (under Usage)

[mxmlnglt]

Specific GraphQL-related Content-Type header value application/graphql was added last year: #71

However, it seems this hasn't been added in the Usage chapter of the README file, leading probably to people to ignore this:
https://github.com/graphql-java-kickstart/graphql-java-servlet#usage