Use bazel to set the correct source dir

Change-Id: Ie0aa065b8531ea257eac3199fce4867494aa6df5
diff --git a/polygerrit-ui/README.md b/polygerrit-ui/README.md
index 7699808..9ceda8c 100644
--- a/polygerrit-ui/README.md
+++ b/polygerrit-ui/README.md
@@ -89,7 +89,7 @@
 
 ```sh
 $(bazel info output_base)/external/local_jdk/bin/java \
-    -DsourceRoot=/path/to/my/checkout \
+    -DsourceRoot=$(bazel info workspace) \
     -jar bazel-bin/gerrit.war daemon \
     -d $GERRIT_SITE \
     --console-log \