add 'description' for object setting

lib/settings-panel.js

@@ -590,6 +590,11 @@ function elementForObject (namespace, name, value) {
     h3.textContent = getSettingTitle(keyPath, name)
     section.appendChild(h3)
 
+    const descriptionDiv = document.createElement('div')
+    descriptionDiv.classList.add('setting-description')
+    descriptionDiv.innerHTML = getSettingDescription(keyPath)
+    section.appendChild(descriptionDiv);
+
     const div = document.createElement('div')
     div.classList.add('sub-section-body')
     for (const key of sortSettings(keyPath, value)) {

spec/settings-panel-spec.coffee

@@ -163,6 +163,7 @@ describe "SettingsPanel", ->
           barGroup:
             type: 'object'
             title: 'Bar group'
+            description: 'description of bar group'
             properties:
               bar:
                 title: 'Bar'
@@ -215,6 +216,13 @@ describe "SettingsPanel", ->
       # Should be already collapsed
       expect(controlGroups[1].querySelector('.sub-section .sub-section-heading').parentElement.classList.contains('collapsed')).toBe true
 
+    it 'ensures grouped settings can have a description', ->
+      expect(settingsPanel.element.querySelectorAll('.section-container > .section-body')).toHaveLength 1
+      controlGroups = settingsPanel.element.querySelectorAll('.section-body > .control-group')
+      expect(controlGroups).toHaveLength 3
+      expect(controlGroups[0].querySelectorAll('.sub-section > .setting-description')).toHaveLength 1
+      expect(controlGroups[0].querySelector('.sub-section > .setting-description').textContent).toBe 'description of bar group'
+
   describe 'settings validation', ->
     beforeEach ->
       config =