[Keyboard] Add Lemon40 keyboard (#17357)

keyboards/horrortroll/lemon40/rules.mk

@@ -0,0 +1,28 @@
+SRC += lib/bongocat.c
+
+# MCU name
+MCU = atmega32u4
+
+# Bootloader selection
+BOOTLOADER = atmel-dfu
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = yes      # Enable Bootmagic Lite
+MOUSEKEY_ENABLE = no        # Mouse keys
+EXTRAKEY_ENABLE = yes       # Audio control and System control
+CONSOLE_ENABLE = no         # Console for debug
+COMMAND_ENABLE = no         # Commands for debug and configuration
+NKRO_ENABLE = yes           # Enable N-Key Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = yes       # Enable keyboard RGB underglow
+AUDIO_ENABLE = no           # Audio output
+
+# OLED enabled
+OLED_ENABLE = yes
+OLED_DRIVER = SSD1306
+WPM_ENABLE = yes
+
+# Additional thing to reduce compiled size
+LTO_ENABLE = yes