add a brief note to the readme about how to do RequireJS-style optimization

[asutherland]

If I skim the volo "binary", it looks like it might have the RequireJS optimizer goodness inside. I expect that will happen someday, but hasn't happened yet. A brief word in the readme that I should use RequireJS for optimization for now would reassure me that I'm not doing things wrong.

[jrburke]

It is still recommended to use r.js separately, I just use some components in it in volo, mainly the node adapter work and the uglifjs-backed parser module. I'll put a note in the readme, marked this for the 0.2 release since I'm currently working on a branch.