Update Twitter instructions on docs Authorization page

[itsmejoeeey]

Took me too long to understand why a successful Twitter authorization still had the username and avatar blank on my remark42 instance.

Found this page here that helped me understand that new Twitter developer accounts (after November 15th, 2021) need "Elevated access" to access the v1.1 https://api.twitter.com/1.1/account/verify_credentials.json route needed to receive this information.

Twitter accepted me for elevated access after explaining this, and that solved the problem.

The docs should be updated with a note to make this clear. I'll try open a PR soon when I have a spare moment.