PolyGerrit: add --no-results-cache to the example commandline.

Change-Id: I85c5c1d2ad96651a9a46fe9483cd6bb07a007426
diff --git a/polygerrit-ui/README.md b/polygerrit-ui/README.md
index dc0a731..533d13e 100644
--- a/polygerrit-ui/README.md
+++ b/polygerrit-ui/README.md
@@ -57,9 +57,12 @@
 Run all web tests:
 
 ```sh
-buck test --include web
+buck test --no-results-cache --include web
 ```
 
+The `--no-results-cache` flag prevents flaky test failures from being
+cached.
+
 If you need to pass additional arguments to `wct`:
 
 ```sh
@@ -70,4 +73,3 @@
 
 We follow the [Google JavaScript Style Guide](https://google.github.io/styleguide/javascriptguide.xml)
 with a few exceptions. When in doubt, remain consistent with the code around you.
-