package/python: clarify that this refers to the deprecated 2.7 series

Python 2.7 is EOL, so people should use the python3 package instead if
possible.  Make it a bit more obvious that 'python' is not the right package
to use by explicitly mentioning that this is about python 2.7 and that it is
deprecated.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>