Add description in Bluetooth docs for requiring NKRO to be disabled (#10359)

docs/feature_bluetooth.md

@@ -26,7 +26,10 @@ A Bluefruit UART friend can be converted to an SPI friend, however this [require
 
 <!-- FIXME: Document bluetooth support more completely. -->
 ## Bluetooth Rules.mk Options
-Use only one of these
+
+The currently supported Bluetooth chipsets do not support [N-Key Rollover (NKRO)](reference_glossary.md#n-key-rollover-nkro), so `rules.mk` must contain `NKRO_ENABLE = no`.
+
+Use only one of these to enable Bluetooth:
 * BLUETOOTH_ENABLE = yes (Legacy Option)
 * BLUETOOTH = RN42
 * BLUETOOTH = AdafruitBLE

tmk_core/common.mk

@@ -99,11 +99,15 @@ ifeq ($(strip $(COMMAND_ENABLE)), yes)
 endif
 
 ifeq ($(strip $(NKRO_ENABLE)), yes)
-    ifneq ($(PROTOCOL),VUSB)
+    ifeq ($(PROTOCOL), VUSB)
+        $(info NKRO is not currently supported on V-USB, and has been disabled.)
+    else ifeq ($(strip $(BLUETOOTH_ENABLE)), yes)
+        $(info NKRO is not currently supported with Bluetooth, and has been disabled.)
+    else ifneq ($(BLUETOOTH),)
+        $(info NKRO is not currently supported with Bluetooth, and has been disabled.)
+    else
         TMK_COMMON_DEFS += -DNKRO_ENABLE
         SHARED_EP_ENABLE = yes
-    else
-        $(info NKRO is not currently supported on V-USB, and has been disabled.)
     endif
 endif