Add new property and update "is bindable property" (#79)

* Update validationbehavior.md

* Update validationbehavior.md

Author: jfversluis

docs/behaviors/validationbehavior.md

@@ -14,13 +14,14 @@ The ValidationBehavior allows users to create custom validation behaviors. All o
 
 |Property  |Type  |Description  |
 |---------|---------|---------|
-| ForceValidateCommand | [ICommand](xref:System.Windows.Input.ICommand) | Allows the user to provide a custom ICommand that handles forcing validation. |
-| Flags | ValidationFlags | Provides an enumerated value that specifies how to handle validation. |
-| InvalidStyle | [Style](xref:Xamarin.Forms.Style) | The Style to apply to the element when validation fails. |
-| IsValid | bool  | Indicates whether or not the current value is considered valid. |
+| ForceValidateCommand | [ICommand](xref:System.Windows.Input.ICommand) | Allows the user to provide a custom ICommand that handles forcing validation. This is a bindable property. |
+| Flags | ValidationFlags | Provides an enumerated value that specifies how to handle validation. This is a bindable property. |
+| InvalidStyle | [Style](xref:Xamarin.Forms.Style) | The Style to apply to the element when validation fails. This is a bindable property. |
+| IsNotValid | bool  | Indicates whether or not the current value is considered invalid. This is a bindable property. |
+| IsValid | bool  | Indicates whether or not the current value is considered valid. This is a bindable property. |
 | ValidStyle | [Style](xref:Xamarin.Forms.Style) | The Style to apply to the element when validation is successful.  |
-| Value | object | The value to validate. |
-| ValuePropertyName | string | Allows the user to override the property that will be used as the value to validate. |
+| Value | object | The value to validate. This is a bindable property. |
+| ValuePropertyName | string | Allows the user to override the property that will be used as the value to validate. This is a bindable property. |
 
 ## Sample