[tools-amd/en] add AMD / require.js tutorial

This adds a very basic tutorial for JavaScript's AMD spec and require.js, targeted at people using JavaScript on a daily basis.

Since English is not my native language feel free to point out the most awkward phrasings and other mistakes.
Technical input is welcome, too.

On a side note: is it possible to export only a portion of the code blocks included in the document when doing "Get the code"?
I found it rather hard to produce a running example of code when having to explain how to separate code into several files...
If I could only export the first block it would be running just fine, but right now I'd had to resort to using a jsfiddle. 

I'd guess this is probably a problem for other "tools" documents, too.
I don't think the website does line breaking for us so this will need to be broken up if you don't mind.