Updates getting-started.rst

[antoineaws]

Since the latest brew python is now at 3.9.4, it throws errors when executing pip3 install -r requirements.txt. Hence I added a couple lines for notes in case someone runs into these issues. Cheers.

to: @airbnb/binaryalert-maintainers cc: size: small|medium|large resolves #

Background

Documentation enhancement to make sure the correct version of python is installed and if not, where to get python 3.6.x.

Changes

Adds 2 notes to help users in case they run into similar issues.

Testing

Ran the additional commands added to the document locally and it passed.

[coveralls]

Coverage remained the same at 90.52% when pulling 7b9235d7beefd409ce68a6a54e88291a7d5a884a on antawad:patch-1 into a9c0f06affc35e1f8e45bb77f835b92350c68a0b on airbnb:master.