I know some users are getting the "E: Couldn't find package...."
Here's some steps in case anyone has issues:
1. Open /etc/apt/sources.list in your favorite editor.
2. Add the following lines to the list:
deb http://http.kali.org/kali kali main non-free contrib
deb-src http://http.kali.org/kali kali main non-free contrib
3. Write file
4. Open Terminal > apt-get update > apt-get install armitage > service postgresql start > service metasploit start
5. Program should be under /usr/bin