Added not yet complete tools writeup.

We'll want to change this, perhaps do this from the Makefile - since the dev version of dart often fixes things, we'll want both installed - the workflow will be: if something doesn't work with this version of dart tools, try the dart-dev tools next.

I have installed dart and dart-dev into /usr/local, and linked to /Applications.
I also have linked the appropriate sdk/bin command line tools back to /usr/local/bin, so that we don't have problems with PATH.   `dart2js` is from `dart`, and `dart2js-dev` is from `dart-dev`, and so forth.