Documentation: clarify dynamic max_age is ignored with SESAME_MAX_AGE = None (the default)

[silviogutierrez]

I suspected this, as the docs clearly state SESAME_MAX_AGE set to None means we have no timestamps of any kind.

But authenticate and get_user will still happily accept max_age=5 but this will be silently ignored.

Not a huge issue, but given SESAME_MAX_AGE defaults to None, worth clarifying.

Let me know if this makes sense and I can open a docs PR.

Thanks for all the great work on this library.

[aaugustin]

You're supposed to get a warning for this. Are you not seeing the warning?

[silviogutierrez]

You're right, I am. I must have missed it in all the server output.

Thanks again.