Improve the --self-signer help texts and add to the template.

- Fixes 25e99e5afb1e2f382e138a4502c9e00641dd903b.

src/cli/types/cert_designator.rs

@@ -764,9 +764,9 @@ This adds the certificates listed in the configuration file under \
 ",
                         SIGNER_SELF,
                         if let Some(certs) = config::get_augmentation(SIGNER_SELF) {
-                            format!("The following certs will be added: {}.", certs)
+                            format!("The following keys will be added: {}.", certs)
                         } else {
-                            "Currently, the list of certificates to be added is empty."
+                            "Currently, the list of keys to be added is empty."
                                 .into()
                         }),
                 ),

src/config.rs

@@ -286,6 +286,9 @@ impl ConfigFile {
 [encrypt]
 #for-self = [\"fingerprint of your key\"]
 
+[sign]
+#signer-self = [\"fingerprint of your key\"]
+
 [key.generate]
 #cipher-suite = <DEFAULT-CIPHER-SUITE>