adds document about what metrics we are tracking and some comments for each one
adds document about what metrics we are tracking and some comments for each one

dbirchak/CartoDB-SQL-API,dbirchak/CartoDB-SQL-API,calvinmetcalf/CartoDB-SQL-API,calvinmetcalf/CartoDB-SQL-API,calvinmetcalf/CartoDB-SQL-API,calvinmetcalf/CartoDB-SQL-API,dbirchak/CartoDB-SQL-API,dbirchak/CartoDB-SQL-API,CartoDB/CartoDB-SQL-API,CartoDB/CartoDB-SQL-API