Fix SPI2 ncs pin number

README.md

@@ -173,7 +173,7 @@ In order to allocate pins to peripherals there is a nice tool [STM32CubeMX](http
 // sck    - pb10,
 // miso   - pc2,
 // mosi   - pc3,
-// ncs    - pb4,
+// ncs    - pb12,
 ```
 
 Decide on which pins you want to use, and connect the PMW3389 to your MCU. You can connect the `Motion` signal to a free GPIO (its used to generate an interrupt when the sensor detects a motion event, for allowing wake from sleep mode). Likely you don't need this but you can add it in any case.