Updated readme

README.md

@@ -85,8 +85,31 @@ this identifier, and thus point to another segment, just clone it.
 
 ### Semaphores
 
+Semaphores are created with a key and a max count.
+
+    $key = new FileKey(__FILE__);
+    $sem = new Semaphore($key, 2);
+
+    $sem->allocate(); // -> true
+    $sem->allocate(); // -> true
+    $sem->allocate(); // -> false
+    $sem->release();
+
+    $mutex->destroy();
+
 ### Mutexes
 
+A mutex is a semaphore with a max count of 1.
+
+    $key = new FileKey(__FILE__);
+    $mutex = new Mutex($key);
+
+    $mutex->allocate(); // -> true
+    $mutex->allocate(); // -> false
+    $mutex->release();
+
+    $mutex->destroy();
+
 ### Message Queues
 
     $key = new FileKey(__FILE__);