Add "/roblox" command to FAQ

[trolljoe]

Type

• [ ] Rewrite already written documentation.
• [x] Add/remove new pages.

Questions

• [x] Did you preview on your local machine beforehand?
• [x] Did you follow our commit handbook?
• [x] Did you read the Atlas Contribution Guidelines?
• [x] Did you commit to the dev branch and not master?

Describe your pull request

since some people won't/can't join the discord server and roblox not opening is a pretty common issue, i've added it to the FAQ and troubleshooting tab so people can just see the workarounds there