Clarify source information for dsew-cpr

[krivard]

closes #911

Prerequisites:

• Unless it is a documentation hotfix it should be merged against the dev branch
• Branch is up-to-date with the branch to be merged with, i.e. dev
• Build is successful
• Code is cleaned up and formatted

Summary

Give better instructions for how to locate source information on the healthdata.gov site for this dataset.

[capnrefsmmat]

Kind of annoying we have to say this (why can't they publish a big spreadsheet?), but this looks good