docs: document that C & Python are the preferred languages

Blacklist Perl and Shell code in favour of Python for
sake of readability and portability.
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

docs/hacking.html.in

@@ -343,6 +343,36 @@
         Richard Jones' guide to working with open source projects</a>.
     </p>
 
+    <h2><a id="lang">Language Usage</a></h2>
+
+    <p>
+      The libvirt repository makes use of a large number of programming
+      languages. It is anticipated that in the future libvirt will adopt
+      use of other new languages. To reduce the overall burden on developers,
+      there is thus a general desire to phase out usage of some of the
+      existing languages.
+    </p>
+
+    <p>
+      The preferred languages at this time are:
+    </p>
+
+    <ul>
+      <li>C - for the main libvirt codebase. Dialect supported by
+        GCC/CLang only.</li>
+      <li>Python - for supporting build scripts / tools. Code must
+        run with both version 2.7 and 3.x at this time.</li>
+    </ul>
+
+    <p>
+      Languages that should not be used for any new contributions:
+    </p>
+
+    <ul>
+      <li>Perl - build scripts must be written in Python instead.</li>
+      <li>Shell - build scripts must be written in Python instead.</li>
+    </ul>
+
     <h2><a id="tooling">Tooling</a></h2>
 
     <p>