data: Add note on filter performance in folder preferences (bgo#776858)

Author: kaiw

data/ui/preferences.ui

@@ -687,18 +687,47 @@
                               </packing>
                             </child>
                             <child>
-                              <object class="GtkCheckButton" id="checkbutton_folder_filter_text">
-                                <property name="label" translatable="yes">Apply text filters during folder comparisons</property>
+                              <object class="GtkBox">
                                 <property name="visible">True</property>
-                                <property name="can_focus">True</property>
-                                <property name="receives_default">False</property>
-                                <property name="use_underline">True</property>
-                                <property name="xalign">0</property>
-                                <property name="draw_indicator">True</property>
+                                <property name="can_focus">False</property>
+                                <property name="orientation">vertical</property>
+                                <child>
+                                  <object class="GtkCheckButton" id="checkbutton_folder_filter_text">
+                                    <property name="label" translatable="yes">Apply text filters during folder comparisons</property>
+                                    <property name="visible">True</property>
+                                    <property name="can_focus">True</property>
+                                    <property name="receives_default">False</property>
+                                    <property name="use_underline">True</property>
+                                    <property name="xalign">0</property>
+                                    <property name="draw_indicator">True</property>
+                                  </object>
+                                  <packing>
+                                    <property name="expand">False</property>
+                                    <property name="fill">False</property>
+                                    <property name="position">0</property>
+                                  </packing>
+                                </child>
+                                <child>
+                                  <object class="GtkLabel">
+                                    <property name="visible">True</property>
+                                    <property name="can_focus">False</property>
+                                    <property name="margin_left">24</property>
+                                    <property name="label" translatable="yes">Note: enabling text filters may make comparing large files much slower</property>
+                                    <property name="xalign">0</property>
+                                    <style>
+                                      <class name="dim-label"/>
+                                    </style>
+                                  </object>
+                                  <packing>
+                                    <property name="expand">False</property>
+                                    <property name="fill">True</property>
+                                    <property name="position">1</property>
+                                  </packing>
+                                </child>
                               </object>
                               <packing>
-                                <property name="expand">False</property>
-                                <property name="fill">False</property>
+                                <property name="expand">True</property>
+                                <property name="fill">True</property>
                                 <property name="position">2</property>
                               </packing>
                             </child>