docs: add top level introduction

README.md

@@ -3,13 +3,29 @@
 **Disclaimer: This project is currently in an alpha state. Documentation is actively
 being worked on.**
 
+A collection of packages for defining and using type-checked apis with TypeScript.
+
+TypeScript is a very powerful type system layered on top of JavaScript, but lacks type
+information available at runtime. This is not likely to change because it is
+[an explicit non-goal](https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals#non-goals)
+of TypeScript. [io-ts](https://github.com/gcanti/io-ts) fills in this functionality gap.
+[io-ts-http](packages/io-ts-http/README.md) builds on top of `io-ts` to make it possible
+to define codecs that translate between HTTP requests and plain JS objects.
+Additionally, it provides a way to group these codecs into route definitions, and then
+collect the route definitions into an api. The resulting api definitions may then be
+used on the [client](packages/superagent-wrapper/README.md) and
+[server](packages/express-wrapper/README.md) to have type-checked and runtime-validated
+HTTP calls in a standardized manner.
+
+## Getting started
+
 ```sh
 npm install
 npm run build
 npm test
 ```
 
-# License
+## License
 
 This work is published under the Apache 2.0 license.