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

Objective-C.gitignore

@@ -1,6 +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
@@ -10,12 +16,15 @@ build/
 *.perspectivev3
 !default.perspectivev3
 xcuserdata
+
+## Other
 *.xccheckout
 *.moved-aside
-DerivedData
+*.xcuserstate
+
+## Obj-C/Swift specific
 *.hmap
 *.ipa
-*.xcuserstate
 
 # CocoaPods
 #
@@ -24,3 +33,10 @@ DerivedData
 # http://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
 #
 #Pods/
+
+# Carthage
+#
+# Add this line if you want to avoid checking in source code from Carthage dependencies.
+# Carthage/Checkouts
+
+Carthage/Build

Swift.gitignore

@@ -1,6 +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
@@ -10,12 +16,15 @@ build/
 *.perspectivev3
 !default.perspectivev3
 xcuserdata
+
+## Other
 *.xccheckout
 *.moved-aside
-DerivedData
+*.xcuserstate
+
+## Obj-C/Swift specific
 *.hmap
 *.ipa
-*.xcuserstate
 
 # CocoaPods
 #