Clarified sdconfig warning language for SecureDrop 1.8.0
Clarified sdconfig warning language for SecureDrop 1.8.0

I took the liberty to rescue a code comment from the other PR
which might help others to reason about securedrop-admin.

conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop