Add link to upgrading guide to readme
Add link to upgrading guide to readme

timothyp/statesman,pacso/statesman,gocardless/statesman,eljojo/statesman,mkcode/statesmin,div/statesman,gocardless/statesman,image-tester/statesman,pacso/statesman,mmontalvo/statesman,eljojo/statesman,timothyp/statesman,div/statesman,image-tester/statesman,mmontalvo/statesman