Add label for composer picture search paths. Fix #7764

Author: NathanW2

src/ui/qgscomposerpicturewidgetbase.ui

@@ -53,7 +53,7 @@
         <x>0</x>
         <y>0</y>
         <width>310</width>
-        <height>550</height>
+        <height>553</height>
        </rect>
       </property>
       <layout class="QVBoxLayout" name="mainLayout">
@@ -175,6 +175,13 @@
             </property>
            </widget>
           </item>
+          <item>
+           <widget class="QLabel" name="label_3">
+            <property name="text">
+             <string>Image search paths</string>
+            </property>
+           </widget>
+          </item>
           <item>
            <widget class="QComboBox" name="mSearchDirectoriesComboBox">
             <property name="sizeAdjustPolicy">