update README.md

[mitchellmanware]

• [x] How to install via GitHub
• [x] Examples to reflect new function names and output
• [x] New data sources in table
• [x] Citations

[kyle-messier]

• [ ] Update stale vignettes (epa data download is the version before amadeus)

[mitchellmanware]

updating stale vignettes opened in new issue https://github.com/NIEHS/amadeus/issues/96