[boot time] elinux wiki page for Unified Boot Log was created

Hey everyone,

I've created a page on the elinux wiki for information, discussion, and data
dumping about the "Unified Boot Log" we discussed in our meeting today.

Here is the page:
https://elinux.org/Unified_Boot_Log

Right now, it's just my own mind dump of what I think we're referring to,
and some of the requirements and design elements that I think are
worth discussing.

Feel free to raise questions about the content now, or we can discuss it
in our (special) Boot-time SIG call on May 20th on this topic.
 -- Tim