add README & LinuxCNC setup instructions

README.md

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+# CNC Mill - Diadrive 2000
+
+The entropia got a CNC mill lent, it is a "Diadrive 2000".
+
+This repository contains information on how to setup the mill with a LinuxCNC system and some other QoL tooling.
+
+## G-Code optimizer
+
+`optimize` contains a G-Code optimizer. See [README](./optimize/README).
+
+## Eagle G-Code generator
+
+`pcb2gcode` contains tooling to get a compatible G-Code file from eagle to mill printed circuit boards.
+
+## Mill driver & LinuxCNC setup
+
+`linuxcnc` contains an additional driver required for the mill and some LinuxCNC config foo. Checkout [the README.md](./linuxcnc/README.md) in the folder for further instructions.

linuxcnc/README.md

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+# LinuxCNC
+
+LinuxCNC is a real time operating system that can directly interface with the mills parallel port. The mill itself does not provide any controller.
+
+`hal` contains a custom driver to speak with the mills spindel.
+
+`config` contains a dump of the initial LinuxCNC configuration files we confirmed to be working.
+
+Some more (unsorted) information in german can be found in the [wiki of entropia](https://entropia.de/CNC-Fr%C3%A4se).
+
+## Setting up LinuxCNC
+
+⚠️ The mill requires a parallel port to talk to LinuxCNC! USB-Adapters most likely will not work.
+
+### 1. Installing the OS
+
+1. Download the LinuxCNC ISO from the official webpage [linuxcnc.org/downloads/](https://linuxcnc.org/downloads/). (Last version confirmed working: `2.8.4`)
+2. Create a bootable USB stick from the ISO.
+3. Boot from the stick and setup LinuxCNC (it is a modified debian).
+
+### 2. Stepconfig
+
+Now we need to setup the stepconfig, some basic settings for LinuxCNC to get to know the mill.
+
+1. Open the "Stepconf Wizard" (hidden in the LinuxCNC menu). 
+2. Follow the wizard, you can copy the values from [diadrice2000.stepconf](./config/diadrive2000.stepconf).
+
+Pin assignments are as follows:
+
+| PIN   | Functionality                                      |
+| ----- | -------------------------------------------------- |
+| 1     | unused                                             |
+| 2     | x step                                             |
+| 3     | x direction                                        |
+| 4     | y step                                             |
+| 5     | y direction                                        |
+| 6     | z step                                             |
+| 7     | z direction                                        |
+| 8     | spindle on/off                                     |
+| 9     | coolant (air in our case, controls the compressor) |
+| 10    | minimum + limit x                                  |
+| 11    | maximum + limit z                                  |
+| 12    | minimum + limit y                                  |
+| 13    | unused                                             |
+| 14    | unused (custom driver uses this as clock)          |
+| 15    | unused                                             |
+| 16    | unused (custom driver uses this as data)           |
+| 17    | unused (custom driver uses this as select)         |
+| 18-26 | unused/GND                                         |
+
+⚠️ The x axis must be inverted, you can simply tick the "invert" checkbox for the corresponding pin. 
+
+### 3. Install custom driver
+
+LinuxCNC can talk natively to the axis and endstops, though the spindle is controlled via a SPI interface which LinuxCNC is not capable of. Therefore, we need to load a custom driver into LinuxCNC.
+
+1. Checkout this repository on the LinuxCNC machine.
+2. Open a terminal and navigate into `linuxcnc/hal`. Execute the following command to compile and load the driver: 
+
+```
+halcompile --install spigen.c
+```
+3. Now we need to wire up the custom driver with data from LinuxCNC, open `/home/linuxcnc/configs/diadrive2000/diadrive2000.hal` (might be named differently depending on how you did name the mill in LinuxCNC).
+4. Copy the blocks with a `# SPI spindle` comment from this repositories [diadrive2000.hal](./config/diadrive2000/diadrive2000.hal) to the opened file. This will ensure data will be send to our custom driver and from there to the parallel port pins.
+
+### 4. Setting home position
+
+1. Open the `/home/linuxcnc/configs/diadrive2000/diadrive2000.ini` file and add the `HOME_OFFSET` setting as done in this repositories [diadrive2000.ini](./config/diadrive2000/diadrive2000.ini) file. This will ensure the mill will set the home position 5 mm away from the endswitches, avoiding triggering them under normal operation (and therefore bringing the mill to a stop).