Update nacl.config docs to use key value instead of 'None'

Fixes #27605

Author: rallytime

salt/modules/nacl.py

@@ -39,7 +39,7 @@
 
     cat /etc/salt/master.d/nacl.conf
     nacl.config:
-        key: None
+        key: 'cKEzd4kXsbeCE7/nLTIqXwnUiD1ulg4NoeeYcCFpd9k='
         keyfile: /root/.nacl
 
 When the key is defined in the master config you can use it from the nacl runner:

salt/runners/nacl.py

@@ -15,7 +15,7 @@
 
     cat /etc/salt/master.d/nacl.conf
     nacl.config:
-        key: None
+        key: 'cKEzd4kXsbeCE7/nLTIqXwnUiD1ulg4NoeeYcCFpd9k='
         keyfile: /root/.nacl
 
 Now with the config in the master you can use the runner nacl like: