Change rules_cc badge to only show master branch status

RELNOTES: None.
PiperOrigin-RevId: 230198892
diff --git a/README.md b/README.md
index afc6fc2..6456173 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # C++ rules for Bazel
 
-[![Build status](https://badge.buildkite.com/f03592ae2d7d25a2abc2a2ba776e704823fa17fd3e061f5103.svg)](https://buildkite.com/bazel/rules-cc)
+[![Build status](https://badge.buildkite.com/f03592ae2d7d25a2abc2a2ba776e704823fa17fd3e061f5103.svg?branch=master](https://buildkite.com/bazel/rules-cc)
 
 This repository contains Starlark implementation of C++ rules in Bazel.