doc: FAQ link broken

[srl295]

FAQ link in readme.md is broken

[srl295]

I was going to add to the FAQ that

• createToken can take a full URL or a relative uRL from server base (/callback?foo=bar)
• createToken can only be called once with a certain URL, calling twice will return an invalid grant error

[ATREAY]

hey @srl295, can I work on this issue if it is still open?