added documentation

README.md

@@ -74,6 +74,7 @@ check if given string is valid
 | email | | verify e-mail address | 
 | floating | | test if string contains a parsable floating-point value |
 | integer | | test if string contains a parsable integer value |
+| iban | | verify IBAN (International Bank Account Number) |
 | ip | | verify IP addresses |
 | | .v4 | look for IPv4 addresses only |
 | | .v6 | look for IPv6 addresses only |