[Lock] Add classes's link

Add link to Link and Key classes

Author: mohamedGasmii

components/lock.rst

@@ -77,7 +77,7 @@ method can be safely called repeatedly, even if the lock is already acquired.
 Serializing Locks
 ------------------
 
-The ``Key`` contains the state of the ``Lock`` and can be serialized. This
+The :class:`Symfony\\Component\\Lock\\Key` contains the state of the :class:`Symfony\\Component\\Lock\\Lock` and can be serialized. This
 allows the user to begin a long job in a process by acquiring the lock, and
 continue the job in another process using the same lock::