message: Add: wallet object documentation `chainId` prop
diff: @@ -8,6 +8,7 @@ WalletInstance {
  * Props
  */
  address: String,
  + chainId: Number,
  keystore: Promise<String>,
  mnemonic: String,
  derivationPath?: Promise<String>,
  @@ -35,6 +36,7 @@ _**Example:** Instantiating a software wallet using an existing `privateKey` wil
  * Wallet Object Instance
  * Props
  * [`address`](#address)
  + * [`chainId`](#chainid)
  * [`keystore`](#keystore)
  * [`mnemonic`](#mnemonic)
  * [`derivationPath`](#derivationpath)
  @@ -71,6 +73,26 @@ const wallet = await open({ privateKey: `0x9274...f447` });
  console.log(wallet.address); // 0x3953...a4CC
  ```
  +### `chainId`
  +```js
  +WalletInstance.chainId: Number
  +```
  +
  +Contains the `id` of the network the wallet is intended to work on _(eg: `homestead`, `ropsten`, etc)_.
  +
  +This is used on the hardware wallets to determine the `derivationPath` and on _all_ wallet types as a default if one isn't provided to the object of transaction you wish to [sign](#sign).
  +
  +_**Note:** For the [Metamask Wallet](api-metamask.md) this is not available as it handles it internally, but can be changed using the UI._
  +
  +**Usage:**
  +```js
  +import { open } from 'colony-wallet/ledger';
  +
  +const wallet = await open({ chainId: 3 });
  +
  +console.log(wallet.chainId); // 3
  +```
  +
  ### `keystore`
  ```js
  WalletInstance.keystore: Promise<String>
  