Update README.md

SyncPrim/README.md

@@ -6,3 +6,4 @@ This chapter describes synchronization primitivies in the Linux kernel.
 * [Queued spinlocks](https://0xax.gitbooks.io/linux-insides/content/SyncPrim/sync-2.html) - the second part describes another type of spinlocks - queued spinlocks.
 * [Semaphores](https://0xax.gitbooks.io/linux-insides/content/SyncPrim/sync-3.html) - this part describes implementation of `semaphore` synchronization primitive in the Linux kernel.
 * [Mutual exclusion](https://0xax.gitbooks.io/linux-insides/content/SyncPrim/sync-4.html) - this part describes - `mutex` in the Linux kernel.
+* [Reader/Writer semaphores](https://0xax.gitbooks.io/linux-insides/content/SyncPrim/sync-5.html) - this part describes special type of semaphores - `reader/writer` semaphores.