Documentation: Add explanation about AHCI locking

Author: https://github.com/supercomputer7
Commit: 10c747f2be
Pull-request: https://github.com/SerenityOS/serenity/pull/7100
Reviewed-by: https://github.com/linusg

Kernel/Storage/AHCIPort.cpp

@@ -4,6 +4,9 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+// For more information about locking in this code
+// please look at Documentation/Kernel/AHCILocking.md
+
 #include <AK/Atomic.h>
 #include <Kernel/SpinLock.h>
 #include <Kernel/Storage/AHCIPort.h>