In this directory, each individual package should install its
menu files. Although changing them in this directory to change
the menus on your local system may work, the sysadmin (you?)
is best advised to put the local menufiles in /etc/menu, as, 
otherwise your changes are deleted when you upgrade the corresponding
packages. Users may override the system-wide defaults by putting
their menuentry files in ~/.menu.


For the package maintainer that wants to include menu files in his
package:

The files should have the name of the package that's installing it,
and may contain as many lines (menu entries) as is necessary.

For examples, please look in /usr/share/menu/default


Also, in your postinst you should check for the availability of
the update-menus command, and if available, execute it (no
parameters needed).

For more info, please read /usr/share/doc/menu/html