Add subdirectory for practicing design patterns in C++

+ Add example for singleton

cpp/patterns/singleton/singleton.cpp

@@ -0,0 +1,15 @@
+
+#include "singleton.h"
+
+Singleton::~Singleton()
+{
+  // Delete any allocated data, close any opened files, etc..
+}
+
+Singleton &Singleton::getInstance()
+{
+  // Construct a new singleton if it doesnt exist, return it
+  // + If a static Singleton exists already, just return it
+  static Singleton l;
+  return l;
+}