document cssHash option

site/content/docs/04-compile-time.md

@@ -74,6 +74,7 @@ The following options can be passed to the compiler. None are required:
 | `customElement` | `false` | If `true`, tells the compiler to generate a custom element constructor instead of a regular Svelte component.
 | `tag` | `null` | A `string` that tells Svelte what tag name to register the custom element with. It must be a lowercase alphanumeric string with at least one hyphen, e.g. `"my-element"`.
 | `css` | `true` | If `true`, styles will be included in the JavaScript class and injected at runtime. It's recommended that you set this to `false` and use the CSS that is statically generated, as it will result in smaller JavaScript bundles and better performance.
+| `cssHash` | See right | A function that takes a `{ hash, css, name, filename }` argument and returns the string that is used as a classname for scoped CSS. It defaults to returning `svelte-${hash(css)}`
 | `loopGuardTimeout` | 0 | A `number` that tells Svelte to break the loop if it blocks the thread for more than `loopGuardTimeout` ms. This is useful to prevent infinite loops. **Only available when `dev: true`**
 | `preserveComments` | `false` | If `true`, your HTML comments will be preserved during server-side rendering. By default, they are stripped out.
 | `preserveWhitespace` | `false` | If `true`, whitespace inside and between elements is kept as you typed it, rather than removed or collapsed to a single space where possible.