Bug#763671: gnutls-bin descriptions do not contain any mention of certtool

[Guillaume !]

Package: gnutls-bin 
Version: 3.0.22-3+really2.12.20-8+deb7u2

Its a minor annoyment, but its nice when descriptions contain the names
of the main executable of the package so when a script tells you:
certtool: command not found, you can apt-cache search and find the 
package you need to install.

I haven't read the whole debian policy before posting, so it might or
not be an infringement of it.

G