Add discussion where to retrieve a capabilities schema

Table 6.57: Device Resource FileSpec (CurrentSchema) ? element Reference to an XML schema in XSD format  [XMLSchema] that describes the present limitations of the device that can be used without operator intervention. The referenced XML schema SHALL use the XJDF namespace to describe elements and attributes that are defined in the XJDF namespace. See 9.9 Use of XML Schema for Capability Descriptions for details of using XML schema for device capabilities. FileSpec (Schema) ? element Reference to an XML schema in XSD format  [XMLSchema] that describes ... The referenced XML schema SHALL use the XJDF namespace to describe elements and attributes that are defined in the XJDF namespace. See 9.9 Use of XML Schema for Capability Descriptions for details of using XML schema for device capabilities. 9.9 Use of XML Schema for Capability Descriptions Individual devices will never implement the entire XJDF specification. Meaningful communication between a controller and a device is only possible if the controller is aware of the limitations of the device. XJDF does not provide a proprietary method to define device capabilities. Since XJDF is an XML dialect, standard XML tools such as XML schema  [XMLSchema] SHOULD be used to declare the supported features of a device. See ##Ref Device/FileSpec(Schema) and Device/FileSpec(CurrentSchema) for details of providing a device specific schema. ...