General Hosting Advice

[EternalllZM]

Description of the changes

A general advice section about hosting and bot security. Accomplishing the following objectives based off the original issue and discussion with org members:

1. In particular, information about setting resource usage limits
2. This should also come with a note saying that it's not a complete info about every important aspect of system administration
3. Enabling firewall and enabling automatic security updates as an example
4. If anywhere, the hosting advice should be under the hosting information page at the very bottom in the "other" section

Docs referenced are from digitalocean which are commonly used throughout the docs as well as Ubuntu's documentation for unattended-upgrades.

This PR also:

• Fixes a dead URL and some grammar updates.
• Adds a warning about "free hosts".

Closes #3926

Have the changes in this PR been tested?

Yes

Can be viewed at https://red-discordbot-zmrtd.readthedocs.io/en/hosting-instruct/host-list.html