[docs] Document adapter changes required by sveltejs#2394

documentation/docs/80-adapter-api.md

@@ -30,6 +30,7 @@ Within the `adapt` method, there are a number of things that an adapter should d
   - Calls `init`
   - Converts from the platform's request to a [SvelteKit request](#hooks-handle), calls `render`, and converts from a [SvelteKit response](#hooks-handle) to the platform's
   - Globally shims `fetch` to work on the target platform. SvelteKit provides a `@sveltejs/kit/install-fetch` helper for platforms that can use `node-fetch`
+  - Globally shims a function `generateRandomString(bytes: number)`, which returns a base64-encoded cryptographically-secure random string (suitable, for instance, for use in a CSP nonce), with a length given by the `bytes` parameter. Usually this is done with either Node's `crypto` module or the WebCrypto API.
 - Bundle the output to avoid needing to install dependencies on the target platform, if desired
 - Call `utils.prerender`
 - Put the user's static files and the generated JS/CSS in the correct location for the target platform