add doc

Signed-off-by: lance6716 <lance6716@gmail.com>

README.md

@@ -157,6 +157,17 @@ Default:        false
 
 `allowCleartextPasswords=true` allows using the [cleartext client side plugin](https://dev.mysql.com/doc/en/cleartext-pluggable-authentication.html) if required by an account, such as one defined with the [PAM authentication plugin](http://dev.mysql.com/doc/en/pam-authentication-plugin.html). Sending passwords in clear text may be a security problem in some configurations. To avoid problems if there is any possibility that the password would be intercepted, clients should connect to MySQL Server using a method that protects the password. Possibilities include [TLS / SSL](#tls), IPsec, or a private network.
 
+
+##### `allowFallbackToNoTLS`
+
+```
+Type:           bool
+Valid Values:   true, false
+Default:        false
+```
+
+`allowFallbackToNoTLS=true` acts like a `--ssl-mode=mode=PREFERRED` MySQL client as described in [Command Options for Connecting to the Server](https://dev.mysql.com/doc/refman/5.7/en/connection-options.html#option_general_ssl-mode)
+
 ##### `allowNativePasswords`
 
 ```