update README with correct file name and added license key instructions
update README with correct file name and added license key instructions

mozimos/newrelic_aws_cloudwatch_plugin,buluma/newrelic_aws_cloudwatch_plugin,botlink/newrelic_aws_cloudwatch_plugin,Yuji-Yamamoto-Recruit/newrelic_aws_cloudwatch_plugin,airbnb/newrelic_aws_cloudwatch_plugin