rcu: Add advice to PROVE_RCU_REPEATEDLY kernel config parameter

The PROVE_RCU_REPEATEDLY has no "Say Y"/"Say N" advice, so this commit
adds it.
Reported-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

lib/Kconfig.debug

@@ -539,6 +539,10 @@ config PROVE_RCU_REPEATEDLY
 	 disabling, allowing multiple RCU-lockdep warnings to be printed
 	 on a single reboot.
 
+	 Say Y to allow multiple RCU-lockdep warnings per boot.
+
+	 Say N if you are unsure.
+
 config SPARSE_RCU_POINTER
 	bool "RCU debugging: sparse-based checks for pointer usage"
 	default n