add LOGGER option to use rtt

update example readme for debug log. Update bug template to ask for LOG
as well.

examples/make.mk

@@ -75,7 +75,17 @@ else
 	CFLAGS += -Os
 endif
 
-# TUSB Logging option
+# Log level is mapped to TUSB DEBUG option
 ifneq ($(LOG),)
   CFLAGS += -DCFG_TUSB_DEBUG=$(LOG)
 endif
+
+# Logger: default is UART, can be set to RTT
+ifeq ($(LOGGER),rtt)
+	RTT_SRC = lib/SEGGER_RTT
+	
+	CFLAGS += -DLOGGER_RTT
+  INC   += $(TOP)/$(RTT_SRC)/RTT
+  SRC_C += $(RTT_SRC)/RTT/SEGGER_RTT_printf.c
+  SRC_C += $(RTT_SRC)/RTT/SEGGER_RTT.c
+endif