tips for using Github with Unity

- here is advice using for merging project folders between users, in
particular
- using the simple methods reported in this file, I was able to get my
new repo working properly with my Unity folder containing data for the
island, first copied from usb to computer between computer systems (4_1
folder) and converted from 4.1 to 4.3 (4_3 folder); key thing I think is
to watch out for the hidden file .git, (and remove old one) and to make
sure the overall .gitignore has the right things blocked from copy