move information from greatfet wiki to README

README.md

@@ -1,5 +1,5 @@
 # Crocus
-A GreatFET Neighbor for the Nordic nRF24L01+
+A GreatFET Neighbor for the 2.4 GHz wireless band.
 
 Required KiCad dependency:
 
@@ -11,3 +11,32 @@ submodule:
 ```
 git submodule init && git submodule update
 ```
+
+# Background
+
+Crocus is based on the Nordic RF nRF24L01+ and was inspired by [The Next Hope Badge](http://goodfet.sourceforge.net/hardware/nhb12/).
+
+A notable capability of nRF24L01+ is 2 Mbps FSK.  Many 2.4 GHz wireless transceiver ICs (including the CC2400 on Ubertooth One) only support FSK up to 1 Mbps.  See [Promiscuity is the nRF24L01+'s Duty](http://travisgoodspeed.blogspot.com/2011/02/promiscuity-is-nrf24l01s-duty.html) for an excellent trick that can be done with Crocus.
+
+## Usage Instructions
+
+FIXME: We don't have any firmware yet, but we should implement capabilities similar to goodfet.nrf.
+
+## Pin Usage
+
+signal  | pin     | alt1  | alt2
+--------|---------|-------|-----
+SCK     | J1.38   | J2.32 |
+MOSI    | J1.39   | J2.30 |
+MISO    | J1.40   | J2.38 |
+CSN     | via I2C | J1.37 | J1.29
+CE      | via I2C | J2.9  | J2.21
+SDA     | J2.39   |       |
+SCL     | J2.40   |       |
+INT     | J2.4    | J2.34 | J1.36
+
+Alternative pins may be selected with solder jumpers.
+
+## I2C Address
+
+The default I2C address is 0x20.  Alternative addresses in the ranges 0x10-0x2F, 0x50-0x67, or 0x70-0x77 may be selected with solder jumpers.  Refer to the Crocus schematic and to the PCA9674 data sheet for details.