New documentation for develop (#408)

* documentation refactoring

* documentation fixes

* distilled instructions for MDK

* remove deploy TODO after creating PR

* fixes typos

docs/boards/nrf52840_mdk.md

@@ -0,0 +1,47 @@
+# <img alt="OpenSK logo" src="../img/OpenSK.svg" width="200px">
+
+## Nordic nRF52840 MDK
+
+Makerdiary has instructions on their [website](https://wiki.makerdiary.com/nrf52840-mdk-usb-dongle/opensk/). They use a custom script to deploy via DFU.
+
+After general setup, you still need these steps:
+
+1.  Create the hexfile with the firmware.
+
+    ```shell
+    ./deploy.py --board=nrf52840_mdk_dfu --opensk --programmer=none
+    ```
+
+1.  Download the
+    [script](https://github.com/makerdiary/nrf52840-mdk-usb-dongle/blob/master/tools/uf2conv.py)
+    from Makerdiary's GitHub into the OpenSK repository.
+
+1.  Run the script:
+
+    ```shell
+    python3 uf2conv.py -c -f 0xada52840 -o target/opensk.uf2 target/nrf52840_mdk_dfu_merged.hex
+    ```
+
+1.  Boot into DFU mode. Keep the user button pressed on your hardware while
+    inserting it into a USB slot. You should see a bit of red blinking, and then
+    a constant green light.
+
+1.  Your dongle should appear in your normal file browser like other USB sticks.
+    Copy the file `target/opensk.uf2` over.
+
+1.  Replug to reboot.
+
+### Buttons and LEDs
+
+The big, white button conveys user presence to the application. Some actions
+like register and login will make the device blink, asking you to confirm the
+transaction with a button press.
+
+The LED shows the state of the app. There are different patterns:
+
+| Pattern                            | Cause                  |
+|------------------------------------|------------------------|
+| red glow                           | busy                   |
+| red and blue blinking              | asking for touch       |
+| red, green, white pattern for 5s   | wink (just saying Hi!) |
+| constant green                     | DFU mode               |