Clarify intended audience of the language reference folder

[JordanMartinez]

Per Harry's comment about this, this PR adds a note that the language folder's content is not intended for those learning PureScript for the first time.

I could also update the project's readme to clarify that in the Learning section, but I'll wait for further guidance as to how to do that before doing the work. For example, should I include a note near that link that clarifies that? Should the link be relocated to somewhere else on this repo?

[hdgarrood]

I'd like to think a bit more about how I'd like to present this: determining whether behaviour you're seeing is intended or not is just one reason that you might want to use this reference. You might also want to use this reference to double-check the specifics of a language feature if you don't completely remember how it works, or if you've seen some unusual syntax somewhere and you're not sure what it means. It should also be useful if you're trying to write tooling for the language: ideally I think it should be possible to write a parser which agrees with the compiler's parser using just the language reference, for example.

[JordanMartinez]

Ok. Did you want to me to add what you've written above verbatim? Or should I close this PR and let you write something instead?

[hdgarrood]

I don't really like the idea of adding what I've written above verbatim, because the intended audience of that comment was a fellow maintainer (you) whereas the intended audience of anything in this repo should be much wider. After having thought a bit, I also don't think we should try to direct beginners away from this resource quite as strongly as this PR does; it's true that a beginner is very unlikely to get very far with this resource alone, but if it's complementing something that's more of a guide or tutorial (e.g. the book) I think that's useful. For example, I was learning Rust recently and when I decided I wanted to learn things in a different order to how the book presents them, or just if I wanted to read up on a feature I'd just learned about in more detail, I found it very useful to jump between the Rust book and language reference.

Realistically though I'm unlikely to find the time to give this PR/issue the treatment it deserves, so don't wait for me to write something else.

[JordanMartinez]

This never went anywhere, so I'm closing.