added links to document

Adding links to referenced texts gives readers an easy way to go to a referenced document to learn more about it.

For example, when the document says "In General.—Subtitle VI of title 31, United States Code, is amended by adding after chapter 97 the following:", it's helpful to provide the reader with a  link to [Subtitle VI of title 31](https://www.law.cornell.edu/uscode/text/31/subtitle-VI) and [chapter 97](https://www.law.cornell.edu/uscode/text/7/1a#21).

In general, I tried to pick `.gov` sources since it would be the most authoritative source but in some cases `law.cornell.edu` was a better reference. 

I only had enough time to add a couple links but I want to use this pull request as a starting point to inspire others to add more links.