basic usage in readme

Author: progschj

README.md

@@ -3,5 +3,15 @@ ThreadPool
 
 A simple C++11 Thread Pool implementation.
 
-The "legacy" directory contains a version that does not use std::future
-but a custom Result<T> type that has essentially the same functionalty.
+Basic usage:
+```c++
+// create thread pool with 4 worker threads
+ThreadPool pool(4);
+
+// enqueue and store future
+auto result = pool.enqueue([](int answer) { return answer; }, 42);
+
+// get result from future
+std::cout << result.get() << std::endl;
+
+```