Added README.md file

README.md

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+optional
+========
+
+A library for representing optional (nullable) objects in C++.
+
+```cpp
+optional<int> readInt(); // this function may return either an int or a not-an-int
+
+if (optional<int> oi = readInt()) // did I get a real int
+  cout << "my int is: " << *oi;   // use my int
+else
+  cout << "I have no int";
+```
+
+For more information refer to the documentation provided with this library.