Write some useful stuff in the /web README (#94)

* Write some useful stuff in the /web README

* Fix one busted link in new README

* Reorder some README stuff per feedback

web/README.md

@@ -1,24 +1,61 @@
-# Manifold Markets web
+# Manifold Markets web app
 
-## Getting Started
+## Getting started
+
+To run the development server, install [Yarn][yarn], and then in this directory:
 
 1. `yarn` to install all dependencies
-2. `yarn dev:dev` to bring up a local instance, pointing to dev database)
+2. `yarn dev:dev` starts a development web server, pointing at the development database
 3. Your site will be available on http://localhost:3000
 
-(`yarn dev` will point you to prod database)
+Check package.json for other command-line tasks. (e.g. `yarn dev` will point the development server at the prod database. `yarn emulate` will run against a local emulated database, if you are serving it via `yarn serve` from the [`functions/` package][functions-readme].)
 
-### Running with local emulated database and functions
+## Tech stack
 
-1. `yarn serve` first in `/functions` and wait for it to start
+Manifold's website uses [Next.js][nextjs], which is a [React][react]-based framework that handles concerns like routing,
-2. `yarn dev:emulate` will point you to the emulated database
+builds, and a development server. It's also integrated with [Vercel][vercel], which is responsible for hosting the site
+and providing some other production functionality like serving the API. The application code is written exclusively in
+Typescript. Styling is done via CSS-in-JS in the React code and uses [Tailwind][tailwind] CSS classes.
 
-## Formatting
+## Building and deployment
 
-Before committing, run `yarn format` to format your code.
+Vercel's GitHub integration monitors the repository and automatically builds (`next build`) and deploys both the `main`
+branch (to production) and PR branches (to ephemeral staging servers that can be used for testing.)
 
-Recommended: Use a [Prettier editor integration](https://prettier.io/docs/en/editors.html) to automatically format on save
+Parts of the file structure that directly map to HTTP endpoints are organized specially per Next.js's prescriptions:
+
+### /public
+
+These are static files that will be [served by Next verbatim][next-static-files].
+
+### /pages
+
+These are components that [Next's router][next-pages] is aware of and interprets as page roots per their filename,
+e.g. the React component in pages/portfolio.tsx is rendered on the user portfolio page at /portfolio.
+
+### /pages/api
+
+Modules under this route are specially interpreted by Next/Vercel as [functions that will be hosted by
+Vercel][vercel-functions]. This is where the public Manifold HTTP API lives.
+
+## Contributing
+
+Please format the code using [Prettier][prettier]; you can run `yarn format` to invoke it manually. It also runs by
+default as a pre-commit Git hook thanks to the pretty-quick package. You may wish to use some kind of fancy [editor
+integration][prettier-integrations] to format it in your editor.
 
 ## Developer Experience TODOs
 
 - Prevent git pushing if there are Typescript errors?
+
+[react]: https://reactjs.org
+[nextjs]: https://nextjs.org
+[vercel]: https://vercel.com
+[tailwind]: https://tailwindcss.com
+[yarn]: https://yarnpkg.com
+[prettier]: https://prettier.io
+[prettier-integrations]: https://prettier.io/docs/en/editors.html
+[next-static-files]: https://nextjs.org/docs/basic-features/static-file-serving
+[next-pages]: https://nextjs.org/docs/basic-features/pages
+[vercel-functions]: https://vercel.com/docs/concepts/functions/serverless-functions
+[functions-readme]: https://github.com/manifoldmarkets/manifold/blob/main/functions/README.md