release-notes: Add release notes for 0.16.2-rc2

This commit adds the release notes for the Zephyr SDK 0.16.2-rc2
release.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>

Author: stephanosio

release-notes.md

@@ -1,12 +1,10 @@
 # Notes / Changes in various releases
 
-## Zephyr SDK 0.16.2-rc1
+## Zephyr SDK 0.16.2-rc2
 
 - picolibc:
 
-  * Updated to [Picolibc 1.8.1-397-gdc78096232].
-
-[Picolibc 1.8.1-397-gdc78096232]: https://github.com/zephyrproject-rtos/picolibc/tree/dc780962322dbaf2b326305f312721ea8cf7c265
+  * Updated to Picolibc 1.8.2 release.
 
 ## Zephyr SDK 0.16.1