[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>