test(fix): minor fix to address the review comment

liujiongxin · liujiongxin · commit b6b9eb623d85 · 2022-12-12T16:14:36.000-05:00
diff --git a/test-proxy/README.md b/test-proxy/README.md
@@ -21,6 +21,10 @@ cd test-proxy
 mvn clean install
 ```
 
+To build the proxy with an older version of the client, please download the
+source code [here](https://github.com/googleapis/java-bigtable/releases),
+and repeat the build steps mentioned above.
+
 Start the proxy on default port 9999
 
 ```
