[Keyboard] Add nknl7en keyboard (#11590)

* Add nknl7en keyboard

A 70 keys ANSI Layout split keyboard.
Salicylic-acid3

* Update readme.md

The name, photo, and link were wrong, so they have been corrected.

* Update keyboards/nknl7en/keymaps/salicylic/keymap.c

Co-authored-by: Drashna Jaelre <drashna@live.com>

* Update keyboards/nknl7en/keymaps/salicylic/keymap.c

Co-authored-by: Drashna Jaelre <drashna@live.com>

* Update keyboards/nknl7en/keymaps/salicylic/keymap.c

Co-authored-by: Drashna Jaelre <drashna@live.com>

* Update keyboards/nknl7en/keymaps/salicylic/keymap.c

Co-authored-by: Drashna Jaelre <drashna@live.com>

Co-authored-by: Drashna Jaelre <drashna@live.com>

keyboards/nknl7en/rules.mk

@@ -0,0 +1,24 @@
+# MCU name
+MCU = atmega32u4
+
+# Bootloader selection
+BOOTLOADER = caterina
+
+# Build Options
+#   change yes to no to disable
+#
+BOOTMAGIC_ENABLE = lite     # Virtual DIP switch configuration
+MOUSEKEY_ENABLE = yes       # Mouse keys
+EXTRAKEY_ENABLE = yes       # Audio control and System control
+CONSOLE_ENABLE = no         # Console for debug
+COMMAND_ENABLE = no         # Commands for debug and configuration
+# Do not enable SLEEP_LED_ENABLE. it uses the same timer as BACKLIGHT_ENABLE
+SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend
+# if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
+NKRO_ENABLE = no            # USB Nkey Rollover
+BACKLIGHT_ENABLE = no       # Enable keyboard backlight functionality
+RGBLIGHT_ENABLE = yes       # Enable keyboard RGB underglow
+BLUETOOTH_ENABLE = no       # Enable Bluetooth
+AUDIO_ENABLE = no           # Audio output
+
+SPLIT_KEYBOARD = yes