REL_5_4_1: Update README.txt

A close to iso Forth compiler with full documentation.
This a Debian imposed release, of version 5.4.1 of ciforth for 32 bits linux and 64 bits linux only.
The directory dsc contains a digitally signed archive complying with Debian rules.
Newer version are to be found in REL-5-5-0 e REL-5-5-1 REL-6-0-0 tc. They are not "released" in the git sense.
Copy your archive for you system from this directories.

The main system is to be found in
https://github.com/albertvanderhorst/ciforth