Add port bindings table

Author: rigidsh

README.md

@@ -0,0 +1,20 @@
+# Port bindings
+
+| Port          | Action                  |
+| ------------- | -------------           |
+| PIO0_17       | A button                |
+| PIO0_21       | Steam button led        |
+| PIO1_0        | Joystick click          |
+| PIO1_2        | Start button            |
+| PIO1_3        | Right grip              |
+| PIO1_4        | Left bumper             |
+| PIO0_13       | Right trigger click*    |
+| PIO1_14       | Right bumper            |
+| PIO1_19       | Steam button            |
+| PIO1_20       | Select button           |
+| PIO1_21       | Right touch panel click |
+| PIO1_25       | Left grip               |
+| PIO1_26       | Left touch panel click  |
+| PIO1_27       | Left trigger click      |
+
+* Right trigger click also connected to PIO0_1 for activation IAP