Describe application environment modes

[Nex-Otaku]

Design for configuration rebuild is now (as of 2020-11-12):

1. Configuration rebuilds every request and every console command in "dev" environment by default.
2. Configuration DO NOT rebuilds in "prod" environment by default.
3. New project is created in "dev" environment mode.

This is important differences that should be noted somewhere in docs, "Configuration", "Deployment" or "Installation" section.