Update gpg setup section in readme
Update gpg setup section in readme

Ubuntu 18.04 appears to use gpg v2 by default. This change appears to affect the behavior of the --gen-key switch. It no longer allows the selection of a key type, size, or expiration date. Using --full-gen-key resolves this.

eallrich/checkniner,eallrich/checkniner,eallrich/checkniner