Change banner on openapis.org website to point at LF Training rather than OAI-Course

[SensibleWood]

The banner on https://openapis.org currently reads as follows:

Alter this to point to the new course on LF Training: https://training.linuxfoundation.org/express-learning/openapi-fundamentals-lfel1011/. Update the text to something like:

Want to learn more about OpenAPI? Take our new OpenAPI Fundamentals training course

[swaldron58]

Done.