Maintenance message

Signed-off-by: Alan Cha <[email protected]>

README.md

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+# Development on OpenAPI-to-GraphQL has paused. [GraphQL Mesh](https://the-guild.dev/graphql/mesh) is maintaining an [OpenAPI/Swagger handler](https://github.com/ardatan/graphql-mesh/tree/39e8e083cdb5b6e0746a9bdab7cc71555fb40220/packages/loaders/openapi), which is fork of OpenAPI-to-GraphQL. Please find them [here](https://the-guild.dev/graphql/mesh/docs/handlers/openapi).
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