Provide more clear explanation for the usage of the environment variables

[matea16]

A user on Discord had issues with running queries and receving the following error message:

"Write query forbidden on the main! Coordinator needs to enable writing on main by sending RPC message."

After a while he realized the issue was that he's using an env var related to the HA and provided feedback:

In the container I've set the variable MEMGRAPH_MANAGEMENT_PORT=7444, thinking it would be the port to memgraph lab (the logs port). But it actually starts memgraph in a different config (the one with coordinators). Removing the env variable from the container fixes it. 👍
maybe it would make sense to add an env variable to control that port? I don't see it here: https://memgraph.com/docs/database-management/configuration#environment-variables. In the SHOW CONFIG; it's listed as monitoring_port