Reorder note text for clarity

Currently at http://devcenter.wercker.com/articles/services/, the 2 notes are rendered in all caps, and the convenience var name looks part of the var format, hard to notice it's even there.
Avoid uppercasing literal text

E.g. in http://devcenter.wercker.com/articles/services/ the format of `WERCKER_MYSQL_URL` should read `mysql://...` not `MYSQL://...`.

There are similar h5 transforms in footer and navigation which I didn't touch.
Merge pull request #18 from cben/patch-1

Clarify notes about WERCKER_MYSQL_URL, WERCKER_POSTGRESQL_URL