Updates the manual installation docs

Adds the --host argument to the jicofo command, as suggested by exs on irc.

doc/manual-install.md

 Run jicofo:
 ```sh
 cd dist/{os-name}'
-./jicofo.sh --domain=jitsi.example.com --secret=YOURSECRET2 --user_domain=auth.jitsi.example.com --user_name=focus --user_password=YOURSECRET3
+./jicofo.sh --host=127.0.0.1 --domain=jitsi.example.com --secret=YOURSECRET2 --user_domain=auth.jitsi.example.com --user_name=focus --user_password=YOURSECRET3
 ```
 
 ## Deploy Jitsi Meet