SaveTool: add a help marker for the melee effect colour picker.

src/SaveTool/SaveTool_MassViewer_Weapons.cpp

@@ -411,6 +411,8 @@ void SaveTool::drawWeaponEditor(Weapon& weapon) {
         }
 
         ImGui::ColorEdit3("##CustomEffectColourPicker", &weapon.effectColour.x(), ImGuiColorEditFlags_HDR|ImGuiColorEditFlags_Float);
+        ImGui::SameLine();
+        drawHelpMarker("Click the coloured square for the full picker.");
 
         if(!custom_effect) {
             ImGui::EndDisabled();