Possibly use command-line for exporting submission key

[torinthiel]

Describe the change

The page about generating Submission Key first asks user to generate the key using command line, and later to switch to Kleopatra to export the key and get it's fingerprint. It might be nice to use only one tool, if only to reduce cognitive load of using two different ones.

Moving to only Kleopatra would require slight change in generated key, as Kleopatra doesn't support providing key comment which is used by current instructions.

Moving to only command line seems simplier, as both exporting key and getting the fingerprint are simple, one-command operations (gpg --export -a SecureDrop > '/media/amnesia/Transfer Device/SecureDrop.asc and gpg --fingerprint SecureDrop respectively)

How will this impact SecureDrop users?

Less switching between different tools during installation