Define the terms-of-service link type.

This PR defines a `terms-of-service` link type that refers to a document
which contains information about the agreements between a document's provider
and users who wish to use the document provided.

This link type was initially discussed in privacycg/proposals#39
and initially sketched in https://mikewest.github.io/privacy-policy-discovery/.

source

@@ -25991,6 +25991,15 @@ document.body.appendChild(wbr);</code></pre>
      <td class="no"> &middot; </td>
      <td>Gives a tag (identified by the given address) that applies to the current document.</td>
     </tr>
+
+    <tr>
+     <td><code data-x="rel-terms-of-service">terms-of-service</code></td>
+     <td colspan="2"><span>Hyperlink</span></td>
+     <td><em>not allowed</em></td>
+     <td class="no"> &middot; </td>
+     <td class="no"> &middot; </td>
+     <td>Gives a link to information about the agreements between the current document's provider and users who wish to use the document provided.</td>
+    </tr>
    </tbody>
   </table>
 
@@ -27780,6 +27789,17 @@ document.body.appendChild(wbr);</code></pre>
   </div>
 
 
+  <h5>Link Type "<dfn attr-value for="link/rel,a/rel,area/rel"><code
+  data-x="rel-terms-of-service">terms-of-service</code></dfn>"</h5>
+
+  <p>The <code data-x="rel-terms-of-service">terms-of-service</code> keyword may be used with
+  <code>link</code>, <code>a</code>, and <code>area</code> elements. This keyword creates a
+  <span>hyperlink</span>.</p>
+
+  <p>The <code data-x="rel-terms-of-service">terms-of-service</code> keyword indicates that the
+  referenced document contains information about the agreements between the current document's
+  provider and users who wish to use the current document.</p>
+
 
   <h5>Sequential link types</h5>