add code of conduct and update chat room link

appinfo/info.xml

@@ -36,7 +36,7 @@ If you like this application and if you want to support the development:
     </documentation>
     <category>customization</category>
     <website>https://gitnet.fr/deblan/side_menu</website>
-    <discussion>https://matrix.to/#/!GhfQePnOSPYpYEunWM:neutralnetwork.org</discussion>
+    <discussion>https://matrix.to/#/!TFPucDATKODpHNVAtu:neutralnetwork.org?via=neutralnetwork.org</discussion>
     <bugs>https://gitnet.fr/deblan/side_menu/issues</bugs>
     <repository type="git">https://gitnet.fr/deblan/side_menu</repository>
     <screenshot>https://gitnet.fr/deblan/side_menu/raw/branch/master/screenshots/nc19_default_menu.png</screenshot>