message: add instructions for auth integration
diff: +# Blockstack Auth
  +
  +## How to Integrate
  +
  +### Single-page Apps
  +
  +1) Install `blockstack.js`:
  +
  +```bash
  +npm install blockstack --save
  +```
  +
  +2) Import Blockstack into your project
  +
  +```js
  +import blockstack from 'blockstack'
  +```
  +
  +3) Include the logic to (a) request the user to sign in (b) handling the auth response
  +
  +```js
  +if (blockstack.isUserSignedIn()) {
  + blockstack.loadUserData(function(userData) {
  + showProfile(userData.profile)
  + })
  +} else if (blockstack.isSignInPending()) {
  + blockstack.signUserIn(function(userData) {
  + window.location = window.location.origin
  + })
  +}
  +```
  +
  +### Client-server Apps
  +
  +Coming soon.
  +
  +## Examples
  +
  +### Single-page Apps
  +
  +- [Hello, Blockstack](https://github.com/blockstack/blockstack.js/blob/master/tests/browserTests/auth/app.js#L18)
  +
  +### Client-server Apps
  +
  +- [Blockstack Forum](https://forum.blockstack.org)
  