Simple format fix at .index() method page.

I was browsing the documentation and then saw that in http://api.jquery.com/index/ , in the first example inside the detail section, the sentence "We get back the zero-based position of the list item:" was not inside p tags, so I put the sentence inside tags to get it formatted like the other similar sentences.

I think that the commit says that many lines were altered because I'm in windows. If that is a problem, I can try to fix it somehow.

Thanks for the attention.