Add pthread_rwlock_t implementation to the C library

Change-Id: I14d0a112554756a7294a51fe88c1c408a16b5ff1
diff --git a/libc/docs/CHANGES.TXT b/libc/docs/CHANGES.TXT
index 6159047..e72b422 100644
--- a/libc/docs/CHANGES.TXT
+++ b/libc/docs/CHANGES.TXT
@@ -1,7 +1,12 @@
 Bionic ChangeLog:
 -----------------
 
-Differences between current and Android 2.1:
+Differences between current and Android 2.2:
+
+- <pthread.h>: Add reader/writer locks implementation.
+
+-------------------------------------------------------------------------------
+Differences between Android 2.2. and Android 2.1:
 
 - Support FP register save/load in setjmp()/longjmp() on ARMv7 builds.