Documentation: Add missing alternative for plugin in-tree testing

Bug: Issue 12096
Change-Id: I45ec642e089d1ef53b119f7b2ef68d71b45d3025

src/main/resources/Documentation/build.md

diff --git a/src/main/resources/Documentation/build.md b/src/main/resources/Documentation/build.md
index 02e9d71..8a02ff1 100644
--- a/src/main/resources/Documentation/build.md
+++ b/src/main/resources/Documentation/build.md
@@ -70,10 +70,11 @@
   ./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
 ```