Add note for devsupport in Podfile

Summary:
see #13799
Closes #14352

Differential Revision: D5198266

Pulled By: shergin

fbshipit-source-id: 308f7e3b1a8e09e61a87d25b05e6c065e1bb88f8

Author: sunnylqm

docs/IntegrationWithExistingApps.md

@@ -216,6 +216,7 @@ target 'NumberTileGame' do
   # but if not, adjust the `:path` accordingly
   pod 'React', :path => '../node_modules/react-native', :subspecs => [
     'Core',
+    'DevSupport', # Include this to enable In-App Devmenu if RN >= 0.43
     'RCTText',
     'RCTNetwork',
     'RCTWebSocket', # needed for debugging
@@ -243,6 +244,7 @@ target 'swift-2048' do
   # but if not, adjust the `:path` accordingly
   pod 'React', :path => '../node_modules/react-native', :subspecs => [
     'Core',
+    'DevSupport', # Include this to enable In-App Devmenu if RN >= 0.43
     'RCTText',
     'RCTNetwork',
     'RCTWebSocket', # needed for debugging