Description of embedded tokens omits embedded JWT case

[paddybyers]

In https://ably.com/docs/auth/token#embedded it explains how a token may be embedded as a claim within some other JWT. However, the description says that only Ably tokens can be embedded - these are defined elsewhere as being Ably native tokens (ie system-issued via requestToken(). However, it is also possible to embed JWTs. The text needs updating to reflect this.

[mattheworiordan]

Paddy has created a code example at https://gist.github.com/paddybyers/ce0b315471619568e6ce63944b06bc45. I think it's important we include a code example for both an Ably Token and Ably JWT Token