postinst and prerm
The postinst and prerm files are examples of maintainer scripts. They are shell scripts that are executed after installation and before removal, respectively, of the package. In the case of the Ubuntu hello package, they are used to install (and remove) the info file. Go ahead and copy them into the current debian directory.
cp ../../ubuntu/hello-2.1.1/debian/postinst . cp ../../ubuntu/hello-2.1.1/debian/prerm .