Rename Cookbook to How To, add Introduction, update Quick Start

[jtoar]

This PR reorganizes the sidebar so that the doc categories reflect a kind of learning path. In the process, a new doc, Introduction is added (still a bit of a work in progress), the Quick Start is updated, and Cookbook is renamed to How To (corresponding redwoodjs.com update https://github.com/redwoodjs/redwoodjs.com/pull/1017).

Once the intro and quick start are closer to being finished, I'll update the crwa README.md as well.

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[thedavidprice]

Other items to update:

• click on Docs should go to docs/introduction
• click on Logo should go to https://redwoodjs.com/

And some thoughts about improvements to the mobile view (not everything is working):

GoogleChrome-2Apr22_18-06-49.mp4

[jtoar]

@thedavidprice Just watched the video; agree with everything! Wanted to point out one thing about the Deployment breadcrumb link: the reason that doesn't work is there's no deployment index page: https://redwoodjs.com/docs/deploy/index. The reference one works because there is a reference index page: https://redwoodjs.com/docs/index. We could maybe make the breadcrumb link just go to the introduction: https://redwoodjs.com/docs/deploy/introduction.

[thedavidprice]

Hellofa job well done here @jtoar Looking really really solid all around.

Information Architecture
I like that the docs/ link from the home page goes to docs/introduction. But if you manually enter rwjs.com/doc it goes to docs/index Now that I think about that, its probably the right UX.

I suggest EVERY top-level category — e.g. Reference, Deployment, etc. — needs an index page. Several times now I've tried to move between the sections for Deploy providers on smaller screens and the UX is effectively broken. I expected the deploy/introduction to have links to the sections in the Right Sidebar, but it doesn't. And although I'm so used to this Doc, I even got lured into cliking on the links to the Provider websites that I intuitively thought were for sections... (I'm going to change that right. now. And will do the same for Auth.)

Including in Final 1.0.0
To include the new CRWA README in the 1.0.0 relase, I'm adding this next-release-patch milestone.