TTL generation callback information added

readme.md

@@ -89,6 +89,15 @@ If the session cookie has a `expires` date, `connect-redis` will use it as the T
 
 Otherwise, it will expire the session using the `ttl` option (default: `86400` seconds or one day).
 
+```ts
+interface RedisStoreOptions {
+  ...
+  ttl?: number | {(sess: SessionData): number}
+}
+```
+
+`ttl` also has external callback support. You can use it for dynamic TTL generation. It has access to `session` data.
+
 **Note**: The TTL is reset every time a user interacts with the server. You can disable this behavior in _some_ instances by using `disableTouch`.
 
 **Note**: `express-session` does not update `expires` until the end of the request life cycle. _Calling `session.save()` manually beforehand will have the previous value_.