I've made the following changes to improve this guide.

• update title to reference "SDKs" over "clients" as people are more familiar with this term
• highlight other use cases for OpenAPI beyond generating SDKs
• add a link to OpenAPI.Tools so people can discover more tools
• highlight that FastAPI uses OpenAPI 3.1, so tooling needs to support that version
• clarify the sponsors section
• update Stainless domain
• use thenpx command for@hey-api/openapi-ts so it's faster to get started
• fix broken "copy to clipboard" buttons
• simplify right-hand side navigation from 3 to 2 levels
• reference Hey API docs for more details, so it's hopefully easier to maintain this guide
• add a note encouraging people to open an issue if they want us to update the remaining out-of-date references