Simplify hyper-schema overview example caption

...based on review feedback.

Author: handrews

jsonschema-hyperschema.xml

@@ -149,11 +149,9 @@
             </t>
             <figure>
                 <preamble>
-                    The empty schema is a valid hyper-schema, as all schema keywords are optional,
-                    and simply has no effect.  No hyperlinks are applied by default.  The following
-                    fairly minimal non-trivial hyper-schema shows a single link, with the
-                    IANA-registered link relation type "self", that is build from the lone object
-                    field in the instance:
+                    Here is an example hyper-schema that adds a single link, with the
+                    IANA-registered link relation type "self", that is built from an instance
+                    with one known object field named "id":
                 </preamble>
                 <artwork>
 <![CDATA[{