[nearby] Update README to add build env script am: a3eb71b633 am: 2408fda2a8

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2871060

Change-Id: I290853d8a92f22068eab978ac6c74ae1ac148555
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/nearby/README.md b/nearby/README.md
index 2731b3e..0d26563 100644
--- a/nearby/README.md
+++ b/nearby/README.md
@@ -49,6 +49,7 @@
 ```sh
 Build unbundled module using banchan
 
+$ source build/envsetup.sh
 $ banchan com.google.android.tethering mainline_modules_arm64
 $ m apps_only dist
 $ adb install out/dist/com.google.android.tethering.apex