copy-files.sh: ship the vim tutor files
This copies the vimtutor shell script, along with all the vim tutor
files themselves in various languages, into the Git for Windows
distribution.
Since vi(m) is Git's default editor, and vi(m) has a steep learning
curve, shipping the vimtutor will help mitigate some of that difficulty
for new users. After all, they have enough on their plates learning Git,
without being stuck in an editor they do not know how to control, too!
Fixes issue #217.
Signed-off-by: Curtis Rueden <ctrueden@wisc.edu>