Documentation: Add missing alternative for plugin in-tree testing

Bug: Issue 12096
Change-Id: Ie95ea44da1413f153d7c9c8c2b479e601cf6637c
diff --git a/src/main/resources/Documentation/build.md b/src/main/resources/Documentation/build.md
index 38084d6..91cc37a 100644
--- a/src/main/resources/Documentation/build.md
+++ b/src/main/resources/Documentation/build.md
@@ -80,10 +80,11 @@
   ./tools/eclipse/project.py
 ```
 
-To execute the tests run:
+To execute the tests run either one of:
 
 ```
   bazel test --test_tag_filters=@PLUGIN@ //...
+  bazel test plugins/@PLUGIN@:@PLUGIN@_tests
 ```
 
 How to build the Gerrit Plugin API is described in the [Gerrit