[doc] Updating prerequisites documentation

[ivanpovazan]

A minor update to the documentation related to python3 prerequisites.

MAUI scenarios depend on requests module which does not come out-of-the-box with python3 installation, so running pre.py script can result with:

Traceback (most recent call last): 
File "/Users/ivan/repos/performance/src/scenarios/mauiios/pre.py", line 9, in <module> from shared.mauisharedpython import remove_aab_files, install_versioned_maui 
File "/Users/ivan/repos/performance/src/scenarios/shared/mauisharedpython.py", line 3, in <module> import requests 
ModuleNotFoundError: No module named 'requests'

To solve this problem requests module has to be installed manually, as described in the documentation.

[kotlarmilos]

Thanks!

[ivanpovazan]

Markdownlint errors are not related to this change.
Should we try to solve them here?

[cincuranet]

I'll be working on the MD problems. No need to fix it in this PR.