feat(docs): add MkDocs documentation setup with Docker support and restructure markdown files

Signed-off-by: Dominik Willner <th33xitus@gmail.com>

docs/extensions/gcode-shell-command.md

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+# G-Code Shell Command Extension
+
+### Creator of this extension is [Arksine](https://github.com/Arksine).
+
+This is a brief explanation of how to use the shell command extension for Klipper, which you can install with KIAUH.
+
+After installing the extension you can execute linux commands or even scripts from within Klipper with custom commands defined in your printer.cfg.
+
+#### How to configure a shell command:
+
+```shell
+# Runs a linux command or script from within klipper.  Note that sudo commands
+# that require password authentication are disallowed. All executable scripts
+# should include a shebang.
+# [gcode_shell_command my_shell_cmd]
+#command:
+#  The linux shell command/script to be executed.  This parameter must be
+#  provided
+#timeout: 2.
+#  The timeout in seconds until the command is forcably terminated.  Default
+#  is 2 seconds.
+#verbose: True
+#  If enabled, the command's output will be forwarded to the terminal.  Its
+#  recommended to set this to false for commands that my run in quick
+#  succession.  Default is True.
+```
+
+Once you have set up a shell command with the given parameters from above in your printer.cfg you can run the command as follows:
+`RUN_SHELL_COMMAND CMD=name`
+
+Example:
+
+```
+[gcode_shell_command hello_world]
+command: echo hello world
+timeout: 2.
+verbose: True
+```
+
+Execute with:
+`RUN_SHELL_COMMAND CMD=hello_world`
+
+### Passing parameters:
+As of commit [f231fa9](https://github.com/dw-0/kiauh/commit/f231fa9c69191f23277b4e3319f6b675bfa0ee42) it is also possible to pass optional parameters to a `gcode_shell_command`.
+The following short example shows storing the extruder temperature into a variable, passing that value with a parameter to a `gcode_shell_command`, which then, 
+once the gcode_macro runs and the gcode_shell_command gets called, executes the `script.sh`. The script then echoes a message to the console (if `verbose: True`) 
+and writes the value of the parameter into a textfile called `test.txt` located in the home directory.
+
+Content of the `gcode_shell_command` and the `gcode_macro`:
+```
+[gcode_shell_command print_to_file]
+command: sh /home/pi/klipper_config/script.sh
+timeout: 30.
+verbose: True
+
+[gcode_macro GET_TEMP]
+gcode:
+    {% set temp = printer.extruder.temperature %}
+    { action_respond_info("%s" % (temp)) }
+    RUN_SHELL_COMMAND CMD=print_to_file PARAMS={temp}
+```
+
+Content of `script.sh`:
+```shell
+#!/bin/sh
+
+echo "temp is: $1"
+echo "$1" >> "${HOME}/test.txt"
+```
+
+## Warning
+
+This extension may have a high potential for abuse if not used carefully! Also, depending on the command you execute, high system loads may occur and can cause system instabilities.
+Use this extension at your own risk and only if you know what you are doing!