configuration/env_var_processors.rst: explain clearer what resolve: does

[SimonHeimberg]

Out of documentation, I did not understand correctly what %env(resolve:XXX)% does.

My understanding now: in the value of the environment variable XXX, it replaces all parameters (like %yy%). It does NOT call other processors, so x: %env(resolve:XXX)%/zzz with XXX=/aaa/%env(file:FILE_CONTAINING_PATH)%/bb/ does not work.

I do not understand the current explication:
Replaces the string FOO by the value of a config parameter with the same name:
Maybe FOO is replaced by the value of the parameter foo?

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file: configuration/env_var_processors.rst
doc verson: 5.0 (8c2e52a)
tested on: symfony 3.4.37

[javiereguiluz]

I'm closing this as fixed because the original explanation was changed in #13417.