Documentation used to be clear on purpose of global, and the default environment

[lingfish]

Describe the bug
The old documentation used to be clear about what the default environment is when environments=True is (development), and what the purpose of the global environment is.

Texts:

Without any action, your applications by default run in the [development] environment.

And:

There is also the pseudo-envs [default] to provide comprehensive default values and [global] to provide global values to override in any other environment.

I looked high and low, and didn't find these statements in the newer doco, causing my brain to melt a little.

[rochacbruno]

We can bring that part back to the docs

[lingfish]

Would you like me to attempt a PR, or you have it queued on your task list? :)