[Emergency Profile] UC1: sharing emergency information with user's devices

Hello all,

I've added texts regarding UC1 "sharing emergency information with user's
devices" and slight modifications on its requirements to reflect our
discussions in the Wiki pages.

https://www.w3.org/community/websignage/wiki/Web-based_Signage_Player_Emergency_Profile

Please let me know if I have missed important points, and I need your help
on refining the document. :D

If anyone has idea, please don't hesitate to propose your idea.

Thank you.

@In the previous mail, I've said that I will post to the WiKi after
discussion, but, I've posted this use case before email discussion because
I think it would be better to put baseline text for discussion. sorry for
the confusion. ^^;;;;


Regards,..


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