[docs] configuration documentation does not specify the precedence of each method

[danielknell]

• [x] I have searched the issues of this repo and believe that this is not a duplicate.

Issue

https://python-poetry.org/docs/configuration/ specifies which methods are availible to configure poetry, but does not specify the precedence of the options.

e.g. if a value is set via both poetry config, poetry config --local, and an environment variable, the documentation does not specify which method will be picked.

(local trumping global is obvious, but local vs env is less so)

looking at the code it looks like the sources have the following priority (top wins):

• environment var
• ./poetry.toml
• ~/.config/pypoetry/auth.toml
• ~/.config/pypoetry/config.toml

it would be nice to have this formalised so we can be confident it wont change without warning.