Missing Public Key instruction.

[Erez Zarum <erez@icinga.org.il>]

I always used the web to retrieve the gnupg key 
(http://backports.org/debian/archive.key), now it's unavailable.

I use it because sometimes retrieving the key from subkeys is very slow 
and even not responding, There is also a missing section about it in 
"Instructions"

Another note, in "Instructions" there's a typo in "Subscribe to 
secruritry announce mailing list"


Erez.