Tidy Docs: oapi-codegen URL in Readme points to old deepmap URL

[frenchi]

In May 2024 oapi-codegen project moved to it's own org (see: discussion).

This issue is low priority and largely cosmetic because GitHub handles the 302, but still nice to have.

Suggested Fix:

Update references:

• from: https://github.com/deepmap/oapi-codegen/
• to: https://github.com/oapi-codegen/oapi-codegen/