Update content.json

Edit summary, all under "Explore" section of "Search":
* Removed "What is the world searching for?" [DUPLICATE] and added "today" to "What is the world searching for today?" 
* Also removed "Don't want your searches to be tracked?" [also DUPLICATE]. 
* Added section "Have you explored search engines other than Google?"
* Added "exactly" to "How does search work, exactly" to delineate between section preceding it.
Merge pull request #878 from keyboardkat/patch-12

Fixes Bug 1024831 - Add more info on alternative search engines to Search resources page