docs: Add hardware writeups

Author: sbencoding

hardware/critical_flight/README.md

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+# Critical flight (very easy)
+In this challenge we need to open another type of file.
+
+After downloading the challenge files, we get a bunch of `.gbr` files.
+After some additional internet browsing I find out these are called gerber files.
+
+The `community/gerbv` package on archilnux provides the views that can open these files.
+
+After opening the files I see the following:
+
+![Picture of the opened files](all_layers.png "all files opened in gerbv")
+
+Now I decided to hide/unhide layers as that was the only action I knew how to do.
+
+After some trial and error, the following parts of the flag were revealed:
+
+![Picture of first part of flag](flag1.png "Layer with first part of the flag")
+![Picture of first part of flag](flag2.png "Layer with second part of the flag")
+
+The final symbol of the second part was an `@`, which gave me a bit of a hard time, but the flag was submitted.

hardware/critical_flight/all_layers.png

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+# Debug (easy)
+For this challenge we will use saleae-logic2
+
+Now we are back again with a `.sal` file, and I already have a tool to open this from the first challenge.
+
+Now we see 2 signals RX and TX, and from me experimenting with the analyzers from the first challange I had the feeling that this might be a capture of UART communication.
+
+And indeed the assumption is correct, using the `Async Serial` analyzer with 115200 bits/s (a common value for UART communication) I was able to decode the communication and get the flag.
+
+![Picture of decoded signals](flag.png "result of async serial analyzer")

hardware/critical_flight/flag1.png

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+# Timed transmission (very easy)
+For this challange we need to figure out how to open a `.sal` file.
+
+Well, we get this file and some internet searching later I figure out that there's a tool called `saleae-logic2` that can open this file.
+
+On archlinux this can be acquired from the `aur/saleae-logic2` package.
+
+After opening the file I spent quite a bit of time trying the different analyzers, before noticing that the signals themselves form the letters of the flag.
+
+After copying the letters to a txt file I got the flag.
+
+![Picture of file opened in the right tool](flag.png ".sal file opened in saleae logic 2")
+
+Try to convince yourself that you can see the letters `HTB` in the picture above