DOC: settings-via-env-vars somewhat lacking

Description:

( Documentation issue, probably)

We are using env-variables to configure rocket.chat. We noticed that after first start, changing the env variables and restarting the Rocker.Chat won't apply the new values, which is a bit different compared to any other services we are using. Apparently, this document has some stuff missing that could explain how people are supposed to configure Rocket.Chat: https://docs.rocket.chat/guides/administrator-guides/settings-via-env-vars

The doc says "To set a setting you need only to add the env var SETTING_ID=VALUE when starting the server." and then "You can overwrite any setting by setting an environment variable prefixed with: OVERWRITE_SETTING_". We are not quite sure what gets overwritten and why would we want to overwrite anything? This forum post does probably answer the question:
https://forums.rocket.chat/t/server-configuration-version-control-best-practice/238

Why can't we just change the value of the original environment variable - like in any other service? Are we really supposed to first configure rocket.chat using the "plain" environment variables - and if we later need to change the values, we should change the environment variables to start with ""OVERWRITE_SETTING_". Reading the docs, it's a bit hard to find out what's the reasoning for this exceptional way of configuring Rocket.Chat.

As a fix the documentation could at least be enhanced to explain the stuff that the forum post did.

Steps to reproduce:

1. probably not needed for a documentation issue

Expected behavior:

probably not needed for a documentation issue

Actual behavior:

probably not needed for a documentation issue

Server Setup Information:

• Version of Rocket.Chat Server: probably not needed for a documentation issue
• Operating System: probably not needed for a documentation issue
• Deployment Method: probably not needed for a documentation issue
• Number of Running Instances: probably not needed for a documentation issue
• DB Replicaset Oplog: probably not needed for a documentation issue
• NodeJS Version: probably not needed for a documentation issue
• MongoDB Version: probably not needed for a documentation issue

Client Setup Information

• Desktop App or Browser Version: probably not needed for a documentation issue
• Operating System: probably not needed for a documentation issue

Additional context

Relevant logs:

Start with the settings-via-env-vars guide linked in the issue, then read the referenced forum post to understand the distinction between regular environment variables and OVERWRITE_SETTING_. Update the guide to explain why values may not change after restart, when each form should be used, and how the documented behavior should be verified.