add doc-only `substrate` entry point crate (#14581)

* add doc-only substrate entry point crate

* document a few more things

* add more

* fix width

* Update primitives/io/src/lib.rs

Co-authored-by: Gonçalo Pestana <g6pestana@gmail.com>

* add link

* update cargo toml file

* fix sp-io docs

* improve

* small update

* add license

* satisfy license job

* add a line about FRAME

* CI happy now

* make CI more happy

* Let the check run for the whole workspace

* Forward the substrate node again as default run

* update binary names

* upate verison test

* Fix fix fix

* Fix

* rename to substrate-node in more places

* Revert "rename to substrate-node in more places"

This reverts commit 66960f84a1b6f1f7c638b4040e28e9fbabb8adf5.

* fix

* Fix build pipeline

* Fix properly plus add some docs

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Co-authored-by: Gonçalo Pestana <g6pestana@gmail.com>
Co-authored-by: Bastian Köcher <info@kchr.de>