Documentation: Add missing plugin in-tree testing

Change-Id: I1ea64376ad5294558b045865a107c694c682a46e

src/main/resources/Documentation/build.md

diff --git a/src/main/resources/Documentation/build.md b/src/main/resources/Documentation/build.md
index 3dd3a01..49709ef 100644
--- a/src/main/resources/Documentation/build.md
+++ b/src/main/resources/Documentation/build.md
@@ -19,6 +19,13 @@
   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: