Update README to make case and deaths definitions clearer
drwxr-xr-x - .github
-rw-r--r-- 10 .gitignore
-rw-r--r-- 1289 LICENSE
-rw-r--r-- 3162 PROBABLE-CASES-NOTE.md
-rw-r--r-- 24354 README.md
drwxr-xr-x - excess-deaths
drwxr-xr-x - live
-rw-r--r-- 12774079 us-counties.csv
-rw-r--r-- 235376 us-states.csv
-rw-r--r-- 3853 us.csv