Add missing sip bindings

Author: m-kuhn

python/core/auto_generated/layertree/qgslayertreegroup.sip.in

@@ -127,6 +127,11 @@ Find layer IDs used in all layer nodes. Searches recursively the whole sub-tree.
     QgsLayerTreeGroup *findGroup( const QString &name );
 %Docstring
 Find group node with specified name. Searches recursively the whole sub-tree.
+%End
+
+    QList<QgsLayerTreeGroup *> findGroups() const;
+%Docstring
+Find all group layer nodes
 %End
 
     static QgsLayerTreeGroup *readXml( QDomElement &element, const QgsReadWriteContext &context ) /Factory/;