Added first draft of "pins" project

gpio/pins/L4_Green_CS_CSN_PA4.txt

@@ -0,0 +1,12 @@
+For SPI, this is the Chip Select (which enables the data lines.) Typically LOW to enable -- "CSN" is "Chip Select Not".
+
+Generic GPIO uses PA4.
+
+CHECK: "LPTIM2.OUT/ADC1.9/COMP1 IN- COMP2 IN-"
+
+Devices:
+- BME280[SPI] (CS)
+- BMP280[SPI] (CS)
+- NRF24L01[SPI] (CSN)
+- NRF24L02[SPI] (CSN)
+- CC1101[SPI] (CSN)