SummaryTrading volume on India's four top exchanges doubles, driven by smaller citiesTraders shift to crypto from options trading following tighter rulesGovernment is yet to take a view on regulationNAGPUR, India, Feb 25 (Reuters) - Like thousands of his countrymen in far-flung places, flower-shop owner Ashish Nagose has been learning about trading cryptocurrencies by attending classes every weekday for the past two months in his home city of Nagpur in western India.Nagose bought and sold stock...