message: Add: purser-metamask `accountChangeHook` docs filter usage
diff: @@ -124,8 +124,30 @@ Hook into the state change events with a simple callback:
  ```js
  import { accountChangeHook } from '@colony/purser-metamask';
  +const walletChangedCallback = (state) => {
  + console.log(`The State Change Event triggered!`, state);
  +};
  +
  +await accountChangeHook(walletChangedCallback);
  +```
  +
  +Hook into the state change events with filtering:
  +```js
  +import { open, accountChangeHook } from '@colony/purser-metamask';
  +
  +const metamaskInstance = await open();
  +let addressState = metamaskInstance.address;
  +
  const walletChangedCallback = ({ selectedAddress }) => {
  + /*
  + * Note that you can't use `metamaskInstance.address` to compare
  + * since that will always reflect the newly selected address.
  + * It uses the same method `accountChangeHook` internally to achieve this
  + */
  + if (addressState !== selectedAddress) {
  + addressState = selectedAddress;
  console.log(`You changed your wallet. The new address is: ${selectedAddress}`);
  + }
  };
  await accountChangeHook(walletChangedCallback);
  