Clarify

@cjolif and @pruzand, I wrote down what we discussed at the meeting but please take a look anyway.   The first commit adds the missing information and the second just rearranges everything into better sections.

Some points:

* I really fleshed out the section on testing.
* One thing we forgot to talk about was LESS... I know we decided to use Less rather than Stylus but I'm not sure if we also allow plain CSS or not.
* In the first section about end-user requirements, we should probably list which browsers we support.  Anything else?
add requirejs-dupluigins as well? Also I'm not sure we have to say "ibm-js/requirejs-dplugins". It is registered in bower just as requirejs-dpluigins.  Similarly we don't say "requiresjs/requirejs-text".