[1.0] Add part 1 of the Gatsby v1 tutorial

[KyleAMathews]

No description provided.

[KyleAMathews]

This adds an MVP for part 1 of the Gatsby tutorial.

In writing it, I made a number of small code tweaks as well:

• Make gatsby-config.js really and truly not required (there were a few places that expected it still)
• Tweak the development 404 page copy.
• Change gatsby serve-build to just gatsby serve
• Added a default html.js component. The more I think about it, the vast majority of sites won't need to customize their html.js file directly. They'll just add plugins which add head/body components e.g. gatsby-plugin-react-helmet. Manage html meta info with components.

[KyleAMathews]

What's cool is that now to build Gatsby you literally only need one react.js component at src/pages/index.js + the gatsby package. The tutorial is a "from scratch" style tutorial so starts you from a blank directory and builds up from there.

[gatsbybot]

Deploy preview ready!

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[gatsbybot]

Deploy preview ready!

Built with commit 0994473

https://deploy-preview-1107--gatsbyjs.netlify.com

[gatsbybot]

Deploy preview ready!

Built with commit 0994473

https://deploy-preview-1107--gatsbygram.netlify.com

[KyleAMathews]

Link to the tutorial https://deploy-preview-1107--gatsbyjs.netlify.com/tutorial/part-one/

Headed out for a little while then will merge and start working on the next parts. Lemme know if anyone has any comments on the tutorial and code changes.

[KyleAMathews]

Oh and line number highlighting in code blocks. If someone could fix the CSS so the highlight goes all the way across the block I'd really appreciate that. I spent far too long fighting that. CSS...