update docs

docs/20_Checks/check_ssl_certs.md

-# check SNMP data
+# Check ssl certs
 
 ## Introduction
 
@@ -9,6 +9,11 @@ This functionality requires the openssl binary in $PATH.
 
 It sends performace data with count of days left.
 
+Remark:
+
+This is just a local check of the certificate file.
+It cannot detect a revocation at the issuer.
+
 ## Syntax
 
 Start the script with `-h` to get the help.