remote_schema_headers in README.md

[fross]

Hi,

In README.md, the example provided for the bearer token could be updated.

Current example: {"Authorization" = "Bearer: token"}

Desired example: {"Authorization" = "Bearer token"} → the colon : following Bearer is not required

Authorization does not succeed if a colon : is present and an exception is raised (ariadne_codegen.exceptions.IntrospectionError: Failure of remote schema introspection. HTTP status code: 401).

(I've been banging my head over this for the last 2 hours 😊)