Android: Add kvm note for emulator docs

This is needed, otherwise the emulator will not pick up the kvm changes.

Bug: 1105423
Change-Id: I86b9cd1cdc69e4d19d0574a0460e72730961d3d0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3078087
Auto-Submit: Peter Wen <[email protected]>
Reviewed-by: Haiyang Pan <[email protected]>
Commit-Queue: Peter Wen <[email protected]>
Cr-Commit-Position: refs/heads/master@{#909486}
diff --git a/docs/android_emulator.md b/docs/android_emulator.md
index 1a41cae5..d8a1ee5 100644
--- a/docs/android_emulator.md
+++ b/docs/android_emulator.md
@@ -50,6 +50,13 @@
      $ newgrp kvm
    ```
 
+   You need to log out and log back in so the new groups take effect. Or you
+   can use the following on a per-shell basis without logging out:
+
+   ```
+     $ su - $USER
+   ```
+
 #### Running via the test runner
 
 The android test runner can run emulator instances on its own. In doing so, it