The note was note correct when mentioning encodings vs python[3]-codecs.
This change fixes this confusion.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

This describes the proposal outlined in #8520, with a few
additions/modifications:

* Describes the handling of the Python 2 interpreter

* Allows for normal updates of Python 2 libraries that share the same
  Makefile as their Python 3 version

* Mass removal event has a name

Supersedes #8788.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

This adds more details on the PYTHON[3]_PKG_SETUP_* variables, the
filespec format, and the build/install processes in general.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

It was a semi-popular request a while back that I put off for a while.
Here's a quick doc.
I'll update it later as things change and I don't forget.
It also lets other people update if something is wrong.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>