Add instructions to README on installing python-dev on Python 2 and python3-dev on Python 3
Add instructions to README on installing python-dev on Python 2 and python3-dev on Python 3

QingChenmsft/azure-cli,BurtBiel/azure-cli,yugangw-msft/azure-cli,QingChenmsft/azure-cli,samedder/azure-cli,QingChenmsft/azure-cli,samedder/azure-cli,samedder/azure-cli,BurtBiel/azure-cli,yugangw-msft/azure-cli,yugangw-msft/azure-cli,yugangw-msft/azure-cli,yugangw-msft/azure-cli,QingChenmsft/azure-cli,samedder/azure-cli,yugangw-msft/azure-cli