In docs, clarify that mode and theme aren't prefixed with "ace/mode" or "ace/theme"

[drpepper]

It seems obvious in hindsight, but although you give an example of loading an editor with just mode: "xml" instead of mode: "ace/mode/xml", this isn't what you'd expect coming from the Ace documentation itself. It might be worth insisting on the point in the README.

[douglasduteil]

Haha right.

Just noting that without it if ace try to load extra files like /mode-xml.js, /mode-javascript.js

I don't remember why adding the ace prefix is changing everything. If someone can explain this magic trick that would be the README for sure.