added box model to basic css step page
edited text and added box model example image
fixed coding typo in curriculum
Merge pull request #385 from adowns01/fix-typo-in-frontend-curriculum

fixed coding typo in curriculum
Merge branch 'master' of https://github.com/lumberg/docs into lumberg-master
Refer to Boston chapter in build status and deploy URL

All other references to the main RailsBridge organization can stay as long as
the material we're actually using points back to our own stuff.