Added Iso(ish) layout for tada68. (#1924)

- Basic layout with one function layer.
- Added correct mapping for ISO layout into tada68.h.
- Readme for the keymap.

keyboards/tada68/keymaps/isoish/rules.mk

@@ -0,0 +1,21 @@
+# Build Options
+#   change to "no" to disable the options, or define them in the Makefile in 
+#   the appropriate keymap folder that will get included automatically
+#
+BOOTMAGIC_ENABLE = no       # Virtual DIP switch configuration(+1000)
+MOUSEKEY_ENABLE = yes       # Mouse keys(+4700)
+EXTRAKEY_ENABLE = yes       # Audio control and System control(+450)
+CONSOLE_ENABLE = no         # Console for debug(+400)
+COMMAND_ENABLE = yes        # Commands for debug and configuration
+NKRO_ENABLE = yes           # Nkey Rollover - if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
+BACKLIGHT_ENABLE = yes       # Enable keyboard backlight functionality
+MIDI_ENABLE = no            # MIDI controls
+AUDIO_ENABLE = no           # Audio output on port C6
+UNICODE_ENABLE = no         # Unicode
+BLUETOOTH_ENABLE = no       # Enable Bluetooth with the Adafruit EZ-Key HID
+RGBLIGHT_ENABLE = no        # Enable WS2812 RGB underlight.  Do not enable this with audio at the same time.
+SLEEP_LED_ENABLE = no       # Breathing sleep LED during USB suspend
+
+ifndef QUANTUM_DIR
+	include ../../../../Makefile
+endif