Description of code extensions in Link.Create docs

[sloorush]

In the documentation and the wiki, under the subheading "code extensions" in file: https://dyalog.github.io/link/4.0/API/Link.Create/.

It mentions all the file extensions it recognises but does not mention what each is used for. I think we should say what each file extension is used for like .apln- APL namespace etc, or a reference to https://help.dyalog.com/latest/index.htm#UserGuide/Installation%20and%20Configuration/File%20Associations.htm