[docs] add first draft of environment variables guide (#8263)
[docs] add first draft of environment variables guide (#8263)

* [docs] add first draft of environment variables guide

* [docs] fine tune environment variables guide

Co-authored-by: Charlie Cruzan <2953b215c2408c6fcd3f838b7ad96c528f0f09e6@users.noreply.github.com>

* [docs] fine tune environment variables guide

Co-authored-by: Charlie Cruzan <2953b215c2408c6fcd3f838b7ad96c528f0f09e6@users.noreply.github.com>

* [docs] fine tune environment variables guide

Co-authored-by: Charlie Cruzan <2953b215c2408c6fcd3f838b7ad96c528f0f09e6@users.noreply.github.com>

* [docs] fine tune environment variables guide

Co-authored-by: Charlie Cruzan <2953b215c2408c6fcd3f838b7ad96c528f0f09e6@users.noreply.github.com>

* [docs] fine tune environment variables guide

Co-authored-by: Charlie Cruzan <2953b215c2408c6fcd3f838b7ad96c528f0f09e6@users.noreply.github.com>

* [docs] make all expo-constants references link

Co-authored-by: Charlie Cruzan <2953b215c2408c6fcd3f838b7ad96c528f0f09e6@users.noreply.github.com>
exponent/exponent,exponent/exponent,exponentjs/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent,exponent/exponent,exponent/exponent,exponentjs/exponent,exponentjs/exponent