Add a python to list of packages to source install documentation

[embray]

This page gives lists of system packages to install on common Linux distros as prerequisites for installing Sage. E.g.,

# debian (Stretch or newer) / ubuntu
$ sudo apt-get install binutils pixz gcc g++ gfortran make m4 perl tar \
  git patch openssl libssl-dev libz-dev bc libbz2-dev liblzma-dev libgmp-dev \
  libffi-dev libgf2x-dev libcurl4-openssl-dev curl yasm

Although it is mentioned in the docs that some Python is a prerequisite, it shouldn't be assumed (especially when setting up fresh VMs/containers for building Sage) that a Python is actually already installed. So it would be convenient to add to the list.

Depends on #26964

Component: documentation

Reviewer: Michael Orlitzky

Issue created by migration from https://trac.sagemath.org/ticket/28363

[embray]

comment:1

Ticket retargeted after milestone closed

[mkoeppe]

comment:2

python has already been added to build/pkgs/{debian,arch,conda,fedora}.txt in #29053.

#26964 will generate the command lines in the manual.

[mkoeppe]

Dependencies: #26964

[mkoeppe]

comment:3

Outdated, can be closed.

[orlitzky]

Reviewer: Michael Orlitzky