docs: extends docs on how 'cookie' storage can be used

next-themes/README.md

@@ -146,7 +146,7 @@ Let's dig into the details.
 All your theme configuration is passed to ThemeProvider.
 
 - `storageKey = 'theme'`: Key used to store theme setting in the selected storage (see `storage` property below)
-- `storage`: Optional storage configuration. Defaults to 'localStorage'. Can be set to 'localStorage', 'sessionStorage'.
+- `storage`: Optional storage configuration. Defaults to 'localStorage'. Can be set to 'localStorage', 'sessionStorage' or 'cookie'.
 - `defaultTheme = 'system'`: Default theme name (for v0.0.12 and lower the default was `light`). If `enableSystem` is false, the default theme is `light`
 - `forcedTheme`: Forced theme name for the current page (does not modify saved theme settings)
 - `enableSystem = true`: Whether to switch between `dark` and `light` based on `prefers-color-scheme`
@@ -295,6 +295,8 @@ The available storages are:
   - when using localStorage, the theme is synced across tabs and windows
 - `storage='sessionStorage'`
   - when using sessionStorage, the theme is only persisted for the current session, and not synced across tabs and windows
+- `storage='cookie'`
+  - when using cookie storage, the theme is persisted in a cookie. While the value is persisted across tabs and windows, it is not synced in real-time. The theme is updated on the next page load.
 
 ### Without CSS variables