docs: Document the release notes process for contributors

Now that we have built a fairly solid process for dealing with
release notes, we should start pushing for contributors to
provide the relevant information along with their code:
documenting the process is clearly a requirement for this to
happen.

HACKING

@@ -226,6 +226,13 @@ to "tests/.valgrind.supp" in order to suppress the warning:
 (10) Update tests and/or documentation, particularly if you are adding a new
 feature or changing the output of a program.
 
+(11) Don't forget to update the release notes <news.html> by changing
+"docs/news.xml" if your changes are significant. All user-visible changes,
+such as adding new XML elements or fixing all but the most obscure bugs, must
+be (briefly) described in a release notes entry; changes that are only
+relevant to other libvirt developers, such as code refactoring, don't belong
+in the release notes.
+
 There is more on this subject, including lots of links to background reading
 on the subject, on Richard Jones' guide to working with open source projects
 <http://people.redhat.com/rjones/how-to-supply-code-to-open-source-projects/>.

docs/hacking.html.in

@@ -294,6 +294,16 @@
         <p>Update tests and/or documentation, particularly if you are adding
         a new feature or changing the output of a program.</p>
       </li>
+
+      <li>
+        <p>Don't forget to update the <a href="news.html">release notes</a>
+        by changing <code>docs/news.xml</code> if your changes are
+        significant. All user-visible changes, such as adding new XML elements
+        or fixing all but the most obscure bugs, must be (briefly) described
+        in a release notes entry; changes that are only relevant to other
+        libvirt developers, such as code refactoring, don't belong in the
+        release notes.</p>
+      </li>
     </ol>
 
     <p>