Documentation: Add missing plugin standalone and in-tree testing

Bug: Issue 12096
Change-Id: Ib8eec7b2a49304bd525f380c24a777bcc425ac40
diff --git a/src/main/resources/Documentation/build.md b/src/main/resources/Documentation/build.md
index 08ddcdc..68a99eb 100644
--- a/src/main/resources/Documentation/build.md
+++ b/src/main/resources/Documentation/build.md
@@ -68,6 +68,13 @@
   bazel-bin/plugins/@PLUGIN@/@PLUGIN@.jar
 ```
 
+To execute the tests run either one of:
+
+```
+  bazel test --test_tag_filters=@PLUGIN@ //...
+  bazel test plugins/@PLUGIN@:@PLUGIN@_tests
+```
+
 This project can be imported into the Eclipse IDE.
 Add the plugin name to the `CUSTOM_PLUGINS` set in
 Gerrit core in `tools/bzl/plugins.bzl`, and execute: