[web] [docs] [ENG-935] add python2 dep in documentation

Summary:
Add python2 info to documentation

https://linear.app/comm/issue/ENG-935/add-python2-docs

Test Plan: Delete python2 from your machine and re-download it from the url provided. Update to macOS 12.3 and download python from url provided.

Reviewers: varun, palys-swm, karol-bisztyga, atul, ashoat

Reviewed By: varun, ashoat

Subscribers: ashoat, atul, palys-swm, Adrian, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3536