add swift flatbuffers

flatbuffers/Documentation.docc/Resources/code/swift/swift_code_4.swift

@@ -0,0 +1,10 @@
+import FlatBuffers
+import Foundation
+
+func run() {
+  // create a `FlatBufferBuilder`, which will be used to serialize objects
+  let builder = FlatBufferBuilder(initialSize: 1024)
+
+  let weapon1Name = builder.create(string: "Sword")
+  let weapon2Name = builder.create(string: "Axe")
+}