Suggestion: Mention expected errors from "cp -rp ~/.gnupg [/media/disk/name]/gnupg-backup"

[jkbullard]

Thanks for the great protecting-code-integrity.md guide.

When I did cp -rp ~/.gnupg [/media/disk/name]/gnupg-backup on macOS 10.13.2, I got the following errors:

cp: /Users/---/.gnupg/S.gpg-agent.ssh: Operation not supported on socket
cp: /Users/---/.gnupg/S.dirmngr: Operation not supported on socket
cp: /Users/---/.gnupg/S.gpg-agent: Operation not supported on socket
cp: /Users/---/.gnupg/S.gpg-agent.browser: Operation not supported on socket

If they should be ignored, I suggest that you add a note to that effect just below the command line.

[mricon]

Good catch -- the socket files are not in the home directory on Linux, so I didn't see those. I'll add a warning.