Update AWS connection example to show how to set from env var (#9191)
Update AWS connection example to show how to set from env var (#9191)

The trailing `@` wasn't obvious/documented anywhere (and took me some
trial and error to work out) so to save time for the next person let's
add it to the docs
danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,mistercrunch/airflow,cfei18/incubator-airflow,airbnb/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,mistercrunch/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,danielvdende/incubator-airflow,DinoCow/airflow,wooga/airflow,apache/incubator-airflow,apache/incubator-airflow,lyft/incubator-airflow,mrkm4ntr/incubator-airflow,bolkedebruin/airflow,mrkm4ntr/incubator-airflow,dhuang/incubator-airflow,mistercrunch/airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,DinoCow/airflow,wooga/airflow,Acehaidrey/incubator-airflow,sekikn/incubator-airflow,apache/airflow,apache/airflow,DinoCow/airflow,sekikn/incubator-airflow,cfei18/incubator-airflow,airbnb/airflow,dhuang/incubator-airflow,DinoCow/airflow,sekikn/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,cfei18/incubator-airflow,cfei18/incubator-airflow,bolkedebruin/airflow,apache/incubator-airflow,wooga/airflow,mrkm4ntr/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,sekikn/incubator-airflow,danielvdende/incubator-airflow,wooga/airflow,mistercrunch/airflow,airbnb/airflow,apache/airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,bolkedebruin/airflow,nathanielvarona/airflow,bolkedebruin/airflow,mrkm4ntr/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,nathanielvarona/airflow,apache/airflow,apache/airflow,nathanielvarona/airflow,apache/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,airbnb/airflow