all: release v0.51.0

Change-Id: I07d5321c5a7ed7678fffa1192b87fce590bf728a
Reviewed-on: https://code-review.googlesource.com/c/gocloud/+/50030
Reviewed-by: Tyler Bui-Palsulich <tbp@google.com>
diff --git a/CHANGES.md b/CHANGES.md
index a38da88..82e0db4 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,5 +1,13 @@
 # Changes
 
+## v0.51.0
+
+- secretmanager:
+  - add IAM helper for generic resource IAM handle
+- cloudbuild:
+  - migrate to microgen in a major version
+- Various updates to autogenerated clients.
+
 ## v0.50.0
 
 - profiler: