tests: bluetooth: tester: reference autoPTS in README

Reference autoPTS documentation with more details on how to use this
test.

Fixes #1251

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

tests/bluetooth/tester/README

@@ -13,6 +13,9 @@ https://github.com/intel/auto-pts
 The auto-pts is an automation framework for PTS Bluetooth testing tool provided
 by Bluetooth SIG.
 
+See https://docs.zephyrproject.org/latest/guides/bluetooth/index.html for full
+documentation about how to use this test.
+
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