Added readme.

README.md

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+# evga-icx
+
+This program allows you to read temperature sensors off of supported EVGA 30-series iCX3 video cards, as well as control the fans individually.
+
+## Prerequisites
+A supported EVGA 30-series iCX3 card.  I have not done extensive testing but belive this is every model of their:
+* RTX 3060 Ti
+* RTX 3070
+* RTX 3070 Ti
+* RTX 3080
+* RTX 3080 Ti
+* RTX 3090
+* RTX 3090 Ti
+
+The number of fans supported depends, of course, on your particular model.
+
+Access to the `/dev/i2c` device files, which means either:
+* Run as root, or
+* Install udev rules to allow user access. If you have the OpenRGB udev rules installed to control the LEDs you already have this set up.
+
+## Dependencies
+* libi2c-dev
+
+## Building
+`make`
+
+## Usage
+Note that when controlling fans directly through iCX3 they will fall offline from the Nvidia driver and show as 0 RPM until you return them to automatic mode.
+
+```text
+Available options:
+--gpu N      : Control only GPU N instead of all supported cards
+--fan SPEED  : Set all fans at once to SPEED (see below)
+--fanN SPEED : Set fan N (0-3) to SPEED
+    SPEED may be one of the following:
+      'auto' to return the fan to its default control mode
+      N to set the fan to that manual % speed
+      [+/-]N to set that fan to an RPM offset from the GPU-controlled speed
+--reset      : Reset all fans to their default mode
+--sensors    : Print sensor readings even if setting a fan speed
+```
+
+### Examples:
+Read sensors:
+```text
+$ ./evga-icx
+#0: EVGA GeForce RTX 3090 FTW3 Ultra v2 (/dev/i2c-3) @ c:00.0
+Fan 0: 1094 RPM (36/0%, Auto)
+Fan 1: 1164 RPM (38/0%, Auto)
+Fan 2: 1161 RPM (38/0%, Offset)
+Ext. fan: 0 RPM (0/0%, Offset)
+GPU2: 35.8 C
+MEM1: 35.3 C
+MEM2: 35.6 C
+MEM3: 35.9 C
+PWR1: 35.0 C
+PWR2: 35.6 C
+PWR3: 36.3 C
+PWR4: 36.9 C
+PWR5: 36.3 C
+```
+
+Set external fan to follow Nvidia driver controlled speed with a -500 RPM offset:
+
+`evga-icx --fan3 -500`
+
+Set all fans to manual 100%
+
+`evga-icx --fan 100`
+
+Force all fans on card 0 to off except for fan1:
+
+`evga-icx --gpu 0 --fan1 0 --fan2 auto --fan3 0 --fan4 0`
+
+Return fans back to Nvidia driver control:
+
+`evga-icx --reset`
+
+### Future capabilities
+It appears to also be possible to read power and voltage sensors off of the K|NGP|N cards, and possibly even control the onboard OLED screen.  If you have one of these and are willing to help test this please contact me!