Adds new Makefile target to add package to the latex default path
Adds missing MINI-HOWTO-prosper.txt file

Source: https://github.com/fcecagno/masters-ti/blob/master/MINI-HOWTO-prosper.txt

MINI-HOWTO-prosper.txt describes how one can use the "prosper" class to create
presentations.

The described procedure was NOT tested, so I'm not sure if it is up-to-date.
Standardizes README encoding to UTF-8