Include warning on Readme to remove "testEnvironment: 'node'"

[hugoaboud]

Hi!

First of all thank you so much for the work on this preset. Finally I'm able to use jest with adonis.

As I was trying to set it up, I ran into some troubles with our private library, which extends Adonis functionalities. This library requires global[Symbol(ioc.use)] to be set during import, so I was receiving this message:

 TypeError: global[Symbol.for(...)] is not a function

After a few hours of debugging, I've realized jest wasn't loading adonis-environment, which explicitly shares this global on setup.

Turns out I forgot to remove testEnvironment: 'node' from jest.config.ts. Since I'm kinda new to jest this wasn't obvious at first, so I'd like to recommend you include a warning on the README just for safety.

Have a nice week!