docs: add github.com/a-h/rest to projects list

[a-h]

https://github.com/a-h/rest uses kin-openapi to generate OpenAPI 3.0 specs from Go code.

It can also host the Swagger-UI endpoint for the generated OpenAPI spec.

You provide the API routes, and define the types used for requests and responses, and github.com/a-h/rest will generate the OpenAPI 3.0 spec for you.

You can further customise the generated OpenAPI spec by providing additional information, such as descriptions and examples by adding an ApplyCustomSchema method to your types, or by customising the generated OpenAPI spec object directly.