docs: Adding FAQ entry saying TypeScript should be installed locally

[iwis]

On https://eslint.org/docs/user-guide/getting-started there is information that ESLint should be installed locally: "It is also possible to install ESLint globally rather than locally (using npm install eslint --global). However, this is not recommended, and any plugins or shareable configs that you use must be installed locally in either case."

But, I have not found anywhere information that TypeScript must be installed locally for ESLint to work. It took me several hours to figure it out. Such information would be very user friendly especially for novices.

See #2041

[typescript-eslint]

Thanks for the PR, @iwis!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

---

🙏 Please, if you or your company is finding typescript-eslint valuable, help us sustain the project by sponsoring it transparently on https://opencollective.com/typescript-eslint. As a thank you, your profile/company logo will be added to our main README which receives thousands of unique visitors per day.

[bradzacher]

You'll need to format the markdown correctly, and also add a link in the table of contents at the top of the file.

[codecov]

Codecov Report

Merging #2043 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2043   +/-   ##
=======================================
  Coverage   93.91%   93.91%           
=======================================
  Files         172      172           
  Lines        7843     7843           
  Branches     2253     2253           
=======================================
  Hits         7366     7366           
  Misses        217      217           
  Partials      260      260           

Flag	Coverage Δ
#unittest	93.91% <ø> (ø)

[iwis]

I will try to do it tomorrow, because I am still learning ESLint :)