Add Variables Tutorial

[sovdeeth]

This adds a tutorial on variables and options, just doing an overview of the main topics and giving a few small examples. I tried to keep it fairly to-the-point, but I may have rambled a bit at points.

I would love feedback on how it reads, if I missed anything, if anything's poorly worded, etc.
And especially if anyone's an expert on the variables section, I'd love to know if my impression is correct, I've not used it much.

Currently working using more analogy rather than jargon, to make it more accessible.

Also, I copied from the text.html file, so not sure if all the header stuff is as it should be.

Live version at https://www.sovdee.com/skript/variables/

[AyhamAl-Ali]

Related issue:

• 💡 Tutorials Needed #12

[sovdeeth]

Needs a few typo fixes, a bit of rewording, but should be ready for review within the week.
edit, jun 1st: I lied :)

[sovdeeth]

Will move out of draft after re-writing in markdown.