sync up xcode related gitignore files

some details based on #1221

Global/Xcode.gitignore

@@ -1,4 +1,12 @@
+# Xcode
+#
+# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
+
+## Build generated
 build/
+DerivedData
+
+## Various settings
 *.pbxuser
 !default.pbxuser
 *.mode1v3
@@ -8,7 +16,8 @@ build/
 *.perspectivev3
 !default.perspectivev3
 xcuserdata
+
+## Other
 *.xccheckout
 *.moved-aside
-DerivedData
 *.xcuserstate