updated python datasources note to reflect preference for setting environ variable over editing settings.py
updated python datasources note to reflect preference for setting environ variable over editing settings.py

moritz9/redash,jmvasquez/redashtest,ninneko/redash,EverlyWell/redash,vishesh92/redash,M32Media/redash,denisov-vlad/redash,guaguadev/redash,jmvasquez/redashtest,amino-data/redash,hudl/redash,easytaxibr/redash,ninneko/redash,denisov-vlad/redash,alexanderlz/redash,getredash/redash,alexanderlz/redash,rockwotj/redash,crowdworks/redash,EverlyWell/redash,crowdworks/redash,moritz9/redash,44px/redash,guaguadev/redash,hudl/redash,pubnative/redash,M32Media/redash,M32Media/redash,useabode/redash,akariv/redash,alexanderlz/redash,jmvasquez/redashtest,getredash/redash,denisov-vlad/redash,rockwotj/redash,useabode/redash,jmvasquez/redashtest,vishesh92/redash,useabode/redash,hudl/redash,pubnative/redash,easytaxibr/redash,44px/redash,imsally/redash,stefanseifert/redash,moritz9/redash,pubnative/redash,EverlyWell/redash,rockwotj/redash,EverlyWell/redash,easytaxibr/redash,moritz9/redash,jmvasquez/redashtest,44px/redash,imsally/redash,imsally/redash,amino-data/redash,chriszs/redash,ninneko/redash,hudl/redash,alexanderlz/redash,akariv/redash,guaguadev/redash,stefanseifert/redash,akariv/redash,chriszs/redash,guaguadev/redash,imsally/redash,amino-data/redash,44px/redash,chriszs/redash,amino-data/redash,akariv/redash,stefanseifert/redash,getredash/redash,crowdworks/redash,pubnative/redash,stefanseifert/redash,getredash/redash,rockwotj/redash,ninneko/redash,pubnative/redash,stefanseifert/redash,vishesh92/redash,easytaxibr/redash,guaguadev/redash,ninneko/redash,getredash/redash,denisov-vlad/redash,M32Media/redash,denisov-vlad/redash,useabode/redash,chriszs/redash,crowdworks/redash,vishesh92/redash,easytaxibr/redash,akariv/redash