Align spec's license with group's charter

LICENSE.md

@@ -1,2 +1,3 @@
-All documents in this Repository are licensed by contributors under the [W3C Document
-License](http://www.w3.org/Consortium/Legal/copyright-documents).
+All documents in this Repository are licensed by contributors
+under the
+[W3C Software and Document License](https://www.w3.org/Consortium/Legal/copyright-software).

webrtc.html

@@ -31,14 +31,9 @@
       'https://www.ercim.eu/'><abbr title=
       'European Research Consortium for Informatics and Mathematics'>ERCIM</abbr></a>,
       <a href='https://www.keio.ac.jp/'>Keio</a>, <a href=
-      'https://ev.buaa.edu.cn/'>Beihang</a>). <a href=
-      'https://www.w3.org/Consortium/Legal/copyright-documents'>Document
-      use</a> rules apply. For the entire publication on the W3C site the
-      <a href=
-      'https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer'>liability</a>
-      and <a href=
-      'https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks'>trademark</a>
-      rules apply.
+      'https://ev.buaa.edu.cn/'>Beihang</a>).  W3C <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
+    <a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a rel="license" href="https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document">permissive document license</a> rules
+    apply.
     </p>
     <section id="abstract">
       <p>