Document requestAccessToken property

[tomatualus]

Is your feature request related to a problem? Please describe.
I spent a day and a half trying to get this library working with Azure B2C. The problem is that i only needed an id token but not the access token. To my surprise there is a config value requestAccessToken set to default true. And if i only have setup everything to return only id token, then the code will not work. Because of this code in the tryLoginImplicitFlow method:

Describe the solution you'd like
Either document the property in the README.md or add an example to get only id token..

[jeroenheijmans]

I reckon improvements to docs are always welcome!

I find that it is documented but a tad hidden at OAuthService and in the list of AuthConfig options, but then you have to know that you need it already.

As it might be specific to Azure B2C (?) it could be useful to create docs here specific to that IDS solution?