Running from source: Python 3.6 deprecation warning

[papr]

Python 3.6 has reached its end-of-life on 22 Dec 2016 and with #2251 being merged, there is no need to continue supporting Python 3.6.

We will keep Python 3.6 syntax compatibility until further notice.

[papr]

The current develop branch requires Python 3.7 due to the numpy>=1.20 requirement not providing support for py3.6 any longer.

In addition, #2274 uses asyncio.run() which is only available in Python 3.7 and later.