Update BETA_TESTING.md (#4747)

BETA_TESTING.md

diff --git a/BETA_TESTING.md b/BETA_TESTING.md
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--- a/BETA_TESTING.md
+++ b/BETA_TESTING.md
@@ -1,8 +1,8 @@
 # Beta testing
 
-This page instructs how to test the latest version of DevTools with all experemental features enabled.
+This page describes the fastest way to test the latest version of DevTools with all experemental features enabled. Do not mix this setup with development environment.
 
-If you want to make code changes, follow [contributing guidance](https://github.com/flutter/devtools/blob/master/CONTRIBUTING.md)
+If you want to make code changes, follow [contributing guidance](https://github.com/flutter/devtools/blob/master/CONTRIBUTING.md).
 
 ## Setup and start