uri: Improve wording in book introduction (#5470)

Author: TimWolla

reference/uri/book.xml

@@ -13,10 +13,11 @@
    identify resources on the Internet.
   </simpara>
   <simpara>
-   URI implements RFC 3986, Uniform Resource Identifier (URI): Generic Syntax,
-   which can be found at <link xlink:href="http://www.ietf.org/rfc/rfc3986.txt">http://www.ietf.org/rfc/rfc3986.txt</link>.
-   And WHATWG URL Standard, which can be found at
-   <link xlink:href="https://url.spec.whatwg.org/">https://url.spec.whatwg.org/</link>.
+   This extension implements functionality that follows the
+   <link xlink:href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986,
+   Uniform Resource Identifier (URI): Generic Syntax</link> and
+   <link xlink:href="https://url.spec.whatwg.org/">WHATWG URL Standard</link>
+   specifications.
   </simpara>
  </preface>