update ChangeLog

Change-Id: I05b9ac2cf8fdd26e3f2e68780dca3e613bc2f732
diff --git a/ChangeLog b/ChangeLog
index e146d51..99fb3c0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,5 @@
+deb54d9 Clarify the expected 'config' lifespan in WebPIDecode()
+c7e2d24 update ChangeLog (tag: v0.5.1-rc5)
 c7eb06f Fix corner case in CostManagerInit.
 ab7937a gif2webp: normalize the number of .'s in the help message
 3cdec84 vwebp: normalize the number of .'s in the help message