tessel/npm init instead of mkdir node_modules

[rockbot]

Currently, on the blinky doc page, it instructs the user to mkdir node_modules.

For the sake of consistency across node applications, I recommend that users instead be instructed to either npm init or tessel init. Node users are used to using npm init every time they're starting a new module or application, and starting a new tessel project should be no different.

If the major concern with npm init is that the questions that the init prompts ask are overwhelming to new users, a simple tessel init that creates the package.json for you would also suffice.