doc: update readme for adding binding about skip validate (#1359)

* update readme for adding binding about skip validate

* update readme for adding binding about skip validate

README.md

@@ -572,6 +572,10 @@ $ curl -v -X POST \
 {"error":"Key: 'Login.Password' Error:Field validation for 'Password' failed on the 'required' tag"}
 ```
 
+**Skip validate**
+
+When running the above example using the above the `curl` command, it returns error. Because the example use `binding:"required"` for `Password`. If use `binding:"-"` for `Password`, then it will not return error when running the above example again.
+
 ### Custom Validators
 
 It is also possible to register custom validators. See the [example code](examples/custom-validation/server.go).