openapi: add documentation, small optimisation

README.md

@@ -111,6 +111,8 @@ For **responsible disclosure of vulnerabilities**, please write a mail to the ma
 Etherpad is designed to be easily embeddable and provides a [HTTP API](https://github.com/ether/etherpad-lite/wiki/HTTP-API)
 that allows your web application to manage pads, users and groups. It is recommended to use the [available client implementations](https://github.com/ether/etherpad-lite/wiki/HTTP-API-client-libraries) in order to interact with this API.
 
+OpenAPI (previously swagger) definitions for the API are exposed under `/api/openapi.json`.
+
 # jQuery plugin
 There is a [jQuery plugin](https://github.com/ether/etherpad-lite-jquery-plugin) that helps you to embed Pads into your website.
 

doc/api/http_api.md

@@ -11,6 +11,10 @@ The API is designed in a way, so you can reuse your existing user system with th
 
 Take a look at [HTTP API client libraries](https://github.com/ether/etherpad-lite/wiki/HTTP-API-client-libraries) to check if a library in your favorite programming language is available.
 
+### OpenAPI
+
+OpenAPI (formerly swagger) definitions are exposed under `/api/openapi.json` (latest) and `/api/{version}/openapi.json`. You can use official tools like [Swagger Editor](https://editor.swagger.io/) to view and explore them.
+
 ## Examples
 
 ### Example 1