Feat: comment about single quotes usage for ENCRYPTION_COMMAND config

onionmine.conf.sample

@@ -146,5 +146,9 @@ MINE_ONLY_IF_NO_SELECTED_KEY_EXISTS="1"
 # * ONION_ADDR: contains the Onion Service address of the candidate.
 # * ONION_KEYS_PATH: the path where the key material is stored.
 #
+# Make sure to enclose the command in single quotes so the variables are
+# evaluated only when the command runs and not when the configuration is
+# parsed.
+#
 # The following example uses https://0xacab.org/rhatto/keyringer/
 #ENCRYPTION_COMMAND='keyringer keyring-name encrypt $CONFIG/${ONION_ADDR} ${ONION_KEYS_PATH}'