Update lasagna introduction.md

[depial]

I've brought in more of the about.md since it seems to be more explanatory than what made it into the exercise introduction.md. I think this should address most of the concerns of @BNAndras.

If this seems alright, I can copy this over to the concept introduction.md as well.

[depial]

We could also include a link to the docs on the matter in the about.md.

[colinleach]

I can copy this over to the concept introduction.md as well.

Yes, please.

We could also include a link to the docs

My first thought was yes, we should do it. Then I looked at the page we're linking. A bit heavy for a Basics Concept, perhaps? <<- is for assignment to global variables, which I'm not keen to encourage. Right assign just seems odd, and I don't remember ever seeing it used.

Some things "seemed like a good idea at the time", and have to be kept around for compatibility.

[depial]

I'm fine with leaving the link out since I agree the description is pretty dense.

I think <<- might be a bit more than just global variable assignment, since it seems to be "scope searching" too (for lack of a better term). For example, the times I've found it useful/necessary is for side effects outside of a scope. Here, the assignment is being made to something at the top-level scope (on line 22), and doesn't work otherwise.

In any case, I don't think we need to mention it here, so I'll go ahead and merge.