Add an explanation of what Tag ID, DFP ID, and Tag Name are and what format they should look

[GaryJones]

This may sound trivial but adding an explanation of what Tag ID, DFP ID, and Tag Name are andwhat format they should look (ca-pub-XXXXXXXXXXXXXXXX) like would help tremendously for people like this: http://wordpress.org/support/topic/how-to-get-the-tag-id-dfp-id-tag-name-from-adsense-google-admanager
(and people like me too)

I think it's nearly mandatory in the readme, but it'd also be nice inline on the config page (since large number of people won't read the readme)

Originally posted by @jb510 in #67 (comment)

[GaryJones]

I don't think this is even consistent in the code either, so this needs some deeper subject knowledge to get right.