release_notes.rst: minor update now that 5.16 was released

Harinder's documentation updates also made it into 5.16, so reference
that as well.

Change-Id: I5313faf1218d30a7e3a0b08da78cb8df3939ada4
Signed-off-by: Daniel Latypov <dlatypov@google.com>
diff --git a/release_notes.rst b/release_notes.rst
index 0d17f66..2f03bcf 100644
--- a/release_notes.rst
+++ b/release_notes.rst
@@ -131,8 +131,8 @@
 
 	# property-entry: pass:7 fail:0 skip:0 total:7
 
-5.16 (tentative)
-================
+5.16
+====
 
 - You can filter on test names now in addition to suite names, e.g.
 
@@ -158,6 +158,8 @@
 
 - ``kunit.py`` with ``--raw_output`` will print output in real time.
 
+- In-kernel documentation has been significantly revamped.
+
 5.17 (tentative)
 ================