[FAQ] Add new tip about third party js npm modules

[MaxGraey]

[dcodeIO]

There are kinda two approaches here. First, if the other module is an AS module and published to npm, one can import its sources, effectively creating a combined program, and second, there is host bindings (declares) for everything else, then linking dynamically. Perhaps good to build the paragraph around these two options?

[MaxGraey]

It would be great if you just offer the whole answer. declares should be mentioned in a link, I more prefer avoid a lot of specific details in introduction / FAQ