Create a summary to clarify the different kinds of tokens

[merlinND]

After reading the first few paragraphs of the Hello World guide, I already came across three different kinds of tokens:

• OAuth
• FetchAPI specific authentication token
• Document-specific token (retrieved after sending a document)

It would be great to have a one-stop page to clarify exactly the purpose and usage of each kind of token.

[Neamar]

The first and second one are the same.

But you're right we ought to clarify this somewhere.