Add missing documentation for README.md

README.md

@@ -65,6 +65,7 @@ The name of the session cookie. Defaults to `sessionId`.
 The options object is used to generate the `Set-Cookie` header of the session cookie. May have the following properties:
 * `path` - The `Path` attribute. Defaults to `/` (the root path).
 * `maxAge` - A `number` in milliseconds that specifies the `Expires` attribute by adding the specified milliseconds to the current date. If both `expires` and `maxAge` are set, then `maxAge` is used.
+* `rolling` - Forces the session identifier cookie to be set on every response. The expiration is reset to the original maxAge - effectively resetting the cookie lifetime. This is typically used in conjuction with short, non-session-length maxAge values to provide a quick expiration of the session data with reduced potential of session expiration occurring during ongoing server interactions. Defaults to true.
 * `httpOnly` - The `boolean` value of the `HttpOnly` attribute. Defaults to true.
 * `secure` - The `boolean` value of the `Secure` attribute. Set this option to false when communicating over an unencrypted (HTTP) connection. Value can be set to `auto`; in this case, the `Secure` attribute will be set to false for an HTTP request. In the case of HTTPS, it will be set to true.  Defaults to true.
 * `expires` - The expiration `date` used for the `Expires` attribute. If both `expires` and `maxAge` are set, then `maxAge` is used.