New cookbook entries and their tip counterpart

As promised!

I want to start a discussion on this. Like I said in the wiki, I'm experimenting ember cookbook vs tip format. Check the entry for self-closing tag: although this is a suitable problem-solution case, the problem definition "You're getting a parsing error (unexpected token) from JSX." actually sucks; no one will be able to find it among all the tips, since the error message is too general and they likely will encounter ten different situations with the same error msg.

In this case, it feels a bit forced to fit these stuff in the Q&A format even though intuitively it made sense. The slight disadvantage of the tip counterpart is that there's no searchable* question (but like I just said, the search would be pretty useless because of the large number of entries returned matching the error).