TOPO! readme

To update TOPO! to the latest version:

1) Update to version 4 (file not included in this directory).
2) Update to version 4.28, to allow the subsequent updates to find the software on your computer.
3) update to version 4.50 or 4.502:  I know that 4.50 works, it is what I use; 4.502 supposedly adds support for some newer GPS units, but I have not tested it.