message: Add: wallet object `publicKey` prop documentation
diff: @@ -17,6 +17,7 @@ WalletInstance {
  derivationPath?: Promise<String>,
  privateKey: String,
  privateKeyQR: Promise<String>, // deprecated
  + publicKey: Promise<String>,
  provider: Object, // deprecated
  type: String,
  subtype: String,
  @@ -45,6 +46,7 @@ _**Example:** Instantiating a software wallet using an existing `privateKey` wil
  * [`derivationPath`](#derivationpath)
  * [`privateKey`](#privatekey)
  * [`privateKeyQR`](#privatekeyqr)
  + * [`publicKey`](#publickey)
  * [`provider`](#provider)
  * [`type`](#type)
  * [`subtype`](#subtype)
  @@ -264,6 +266,23 @@ const qr = await wallet.privateKeyQR;
  console.log(qr); // data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAMgAA ... 5rQkAAAAASUVORK5CYII=
  ```
  +### `publicKey`
  +```js
  +WalletInstance.publicKey: Promise<String>
  +```
  +
  +This is a `getter` that returns a `Promise`. Upon resolving, the promise returns the public key for the current address, in `String` form.
  +
  +This is useful for cases where you want to prove the wallet's identity without exposing any private and dangerous information _(eg: `privateKey`, `mnemonic`...)_.
  +
  +```js
  +import { open } from 'colony-wallet/hardware/trezor';
  +
  +const wallet = await open();
  +
  +console.log(await wallet.publicKey); // 0x93f7 ... a9dd
  +```
  +
  ### `provider`
  ```js
  WalletInstance.provider: Object | Function | undefined
  