Update documentation regarding Python 3.9 support (#17611)
Update documentation regarding Python 3.9 support (#17611)


https://github.com/apache/airflow#requirements


danielvdende/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,apache/airflow,bolkedebruin/airflow,apache/incubator-airflow,lyft/incubator-airflow,cfei18/incubator-airflow,mistercrunch/airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,apache/airflow,apache/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,mistercrunch/airflow,mistercrunch/airflow,apache/incubator-airflow,apache/airflow,lyft/incubator-airflow,apache/airflow,danielvdende/incubator-airflow,apache/incubator-airflow,Acehaidrey/incubator-airflow,nathanielvarona/airflow,cfei18/incubator-airflow,Acehaidrey/incubator-airflow,bolkedebruin/airflow,nathanielvarona/airflow,bolkedebruin/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,apache/airflow,nathanielvarona/airflow,apache/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow