Update README.md

updated info for 

Src in dataset from CSV is equal to net in dataset from JSON.
Eqid in dataset from CSV is equal to code in dataset from JSON.
time in dataset from CSV is equal to time in dataset from JSON.
Lat in dataset from CSV is equal to longitude in dataset from JSON.
Lon in dataset from CSV is equal to longitude in dataset from JSON.
Depth in dataset from CSV is equal to depth in dataset from JSON.
nst in dataset from CSV is equal to nst in dataset from JSON.
region in dataset from CSV is equal to place in dataset from JSON.
Merge pull request #12 from taywon/patch-1

Add column mappings to README.md