Added first draft of "pins" project

gpio/pins/L5_Brown_SCK_RTS_PB3.txt

@@ -0,0 +1,13 @@
+For SPI, this is the Serial Clock (which says when to read/write data.) Typically Mode 0 (Idle LOW, Sample Rising Edge, Shift Falling Edge.)
+
+Generic GPIO uses PB3.
+
+CHECK: "ADC1.9/COMP1 IN- COMP2 IN-/SWO"
+
+
+Devices:
+- BME280[SPI] (SCK)
+- BMP280[SPI] (SCK)
+- NRF24L01[SPI] (SCK)
+- NRF24L02[SPI] (SCK)
+- CC1101[SPI] (SCLK)