nano: make nanorc world readable

nano: make nanorc world readable

If file /etc/nanorc is readable by everyone, "default" settings
are available for users as well without necessarily requiring
their own customized .nanorc in their home directory. Or if
they want one, but want it to be based on system's default
nanorc, they can copy it from /etc - without chmodding
file, it is in-accessible for users.

Suggested-by: Oskari Rauta <oskari.rauta@gmail.com>
[switched approach to use INSTALL_DATA]
Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>