Ruby: Don't ignore vendor/Pods/ for Cocoapods, specific to RubyMotion

Ruby.gitignore

@@ -14,11 +14,18 @@
 .dat*
 .repl_history
 build/
-vendor/Pods/
 *.bridgesupport
 build-iPhoneOS/
 build-iPhoneSimulator/
 
+## Specific to RubyMotion (use of CocoaPods):
+#
+# We recommend against adding the Pods directory to your .gitignore. However
+# you should judge for yourself, the pros and cons are mentioned at:
+# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
+#
+# vendor/Pods/
+
 ## Documentation cache and generated files:
 /.yardoc/
 /_yardoc/