README: improve getting started & contributing

[flybayer]

This addresses some things I was first confused by and some common confusions like the .next directory.

It also adds a Contributing and Background & Design Philosophy section.

[rauchg]

Needs rebase since we improved the first section already. The rest should be interesting though!

[flybayer]

@rauchg rebased!

As you can see, I propose abandoning npm run dev in favor of using npm start for development (same as Hyper.app, create-react-app, etc.). Then use scripts.now-start for production. I've found I really like using scripts.now-start because it's very clear what it's for.

[sedubois]

Shouldn't scripts.start be reserved for the production start? Like mentioned here: https://zeit.co/blog/now-static#single-page-applications

[flybayer]

@sedubois, see the *Side Note:* right below that blog post section. As documented here, now will first use now-start and now-build if they're available.

[zpnk]

@flybayer now-start as the production start command may not make sense here given that next can be deployed to any platform.

[rauchg]

Honestly I like the idea of being explicit about development. We routinely get error reports from people trying to launch dev environments to production (not just to now, but really we've seen every PaaS).

This problem is similarly experienced with React, where the default script is the dev build, and production is .min.js, which leads to a lot of people deploying dev code to production or running (and blogging about) inaccurate benchmarks.

[flybayer]

Ok, I've updated this PR to use scripts.dev for development instead of scripts.start.

[rauchg]

I think this could be step 1 or 2, and then we use npm install? Otherwise this overrides the value of --save

[rauchg]

We can still improve the 1,2,3 I think

[flybayer]

@rauchg I reworked the beginning a bit. Do you like this better?

[arunoda]

I'd suggest to add more items to this list.

4. Run npm link to link the local repo to NPM
5. Run npm run build in a new terminal to build and watch for code changes
6. Then npm link this repo inside any example app with npm link next
7. Then you can run your example app with local version of Next.js
   (You may need to re-run example app as you change code in the Next.js repo)

[rauchg]

I believe we've improved this now. A better Contributing section in a different PR would be sweet though