Update README to include loading script example

[atticoos]

It's likely that a common problem will arise when people try to set up the Digits script, as the documentation gives an example of async loading, which will cause problems for Angular trying to load $window.Digits during initialization.

Via #8 we discuss this issue.

[guyschlider]

Hi,

another thing I stumbled when trying to use the module by reading the docs is
that in the demo you are using Digits.AccountFields.Email enum for the account fields, but you are also using the DigitsProvider named as Digits, which doesn't have this property of course.

[atticoos]

Good catch, this was introduced in #6.

For now, you can work around this with $window.Digital.AccountFields.Email -- I'll throw in a patch for this to work properly

[atticoos]

@mp3il I've opened #10 to track the issue