fix: PGP Key should have expiration (#24)

Author: jdauphant-dinum

docs/go-further/setup-security-key.mdx

@@ -348,8 +348,8 @@ Please specify how long the key should be valid.
       <n>w = key expires in n weeks
       <n>m = key expires in n months
       <n>y = key expires in n years
-Key is valid for? (0)
-Key does not expire at all
+Key is valid for? (0) 3y
+Key expires at Jeu  6 avr 11:02:54 2028 CEST
 Is this correct? (y/N) y
 
 GnuPG needs to construct a user ID to identify your key.