Add HOWTOs to the docs site

Add HOWTOs https://github.com/formium/tsdx/issues/379 to the Customization section of the docs site https://github.com/formium/tsdx/issues/379#issuecomment-660387965

[agilgur5]

I’m not sure if Customization is the right section as those are very specific use-cases. I think it would be better in a section called HOWTOs. Crazy name, I know 😆 . Customization could link to that.

That being said, I’m still wary of doing so as:

• Nearly all of them are tsdx.config.js uses, which are super brittle per the warning. Things like #367 that change Rollup’s output.file to output.dir, which is normally internal-only, are now breaking changes due to this exposure 😕 . Making them “official” can exacerbate this
• Not all of them have been verified, like the “local dev” one there should be a way of doing it normally.
• #635 should theoretically solve the issues in a testable and more easily shareable manner, though the kinks still have to be ironed out there on what the API would look like and what the “core plugins” would be (at minimum, they’d be the ones I’ve already written integration tests for due to their frequent usage)

[ambroseus]

@shadiramadan as soon as possible 😃