Provide additional documentation on token management and localStorage

[grokify]

Additional information on token management and localStorage would be useful:

1. Where does the SDK store tokens for multi-tab use? Are tokens stored in localStorage or somewhere else?
2. If tokens are stored in localStorage what is the behavior when localStorage is not available? Is there a fallback or is localStorage required?

Examples or description of the supported localStorage values in the following areas would also be useful:

3. What is an example of localStorage value below for client-side browser use?

var sdk = new SDK({
    localStorage: whatever,

4. What is an example of localStorage value below for server-side Node.js use? For example, could it be an instance of node-localstorage:

RingCentral.SDK.core.Externals.localStorage = Anything;