Add guide on compiling Qt from sources. Add README.

Author: matoushybl

README.md

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+Knowledge base of the Robotics and AI research group
+====================================================
+
+## Installation
+Install `mdbook` by downloading it from [here](https://github.com/rust-lang/mdBook/releases). Alternatively, it can be installed using `cargo install mdbook`.
+
+## Usage
+Run `mdbook serve` to locally create a web server publishing your changes as you write them. When done, commit the changes and the CI will build and publish the book.

src/SUMMARY.md

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 - [Introduction](./intro.md)
 - [Software](./software/intro.md)
+    - [Qt](./software/qt/intro.md)
+        - [Qt on Raspberry Pi](./software/qt/raspberry.md)
 - [Hardware](./hardware/intro.md)
     - [Arduino](./hardware/arduino/intro.md)
         - [Arduino Leonardo](./hardware/arduino/leonardo.md)

src/software/qt/intro.md

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+# QT

src/software/qt/raspberry.md

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+# Getting Qt to work on Raspberry Pi
+
+## Installing from repositories
+
+## Building from source
+This tutorial was inspired by the tutorial [here](https://www.tal.org/tutorials/building-qt-512-raspberry-pi).
+We will be using Qt 5.15 and skipping useless modules. Also gamepad and multimedia with GStreamer should be working out of the box.
+
+Install preprequisities by running
+```bash
+sudo apt-get update
+sudo apt-get install git gdb cmake gcc build-essential libfontconfig1-dev libdbus-1-dev libfreetype6-dev libicu-dev libinput-dev libxkbcommon-dev libsqlite3-dev libssl-dev libpng-dev libjpeg-dev libglib2.0-dev libraspberrypi-dev
+sudo apt-get install libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev gstreamer1.0-plugins-base gstreamer1.0-plugins-good gstreamer1.0-plugins-ugly gstreamer1.0-plugins-bad libgstreamer-plugins-bad1.0-dev gstreamer1.0-pulseaudio gstreamer1.0-tools gstreamer1.0-alsa libasound2-dev pulseaudio libpulse-dev libsdl2-dev libgles2-mesa-dev libgbm-dev libgl1-mesa-dev libglu1-mesa-dev mesa-common-dev libx11-dev
+
+Download the sources from [here](http://download.qt.io/official_releases/qt/) in our case we'll be using `wget` and downloading the 5.15.1 version
+```bash
+wget http://download.qt.io/official_releases/qt/5.15/5.15.1/single/qt-everywhere-src-5.15.1.tar.xz
+```
+
+Decompress the archive by running
+```bash
+tar xf qt-everywhere-src-5.15.1.tar.xz
+```
+
+Setup build configurations for the Raspberry Pi
+```bash
+git clone https://github.com/oniongarlic/qt-raspberrypi-configuration.git
+cd qt-raspberrypi-configuration && make install DESTDIR=../qt-everywhere-src-5.15.1
+cd ..
+```
+
+Prepare the build environment
+```bash
+mkdir -p build
+cd build
+PKG_CONFIG_LIBDIR=/usr/lib/arm-linux-gnueabihf/pkgconfig:/usr/share/pkgconfig ../qt-everywhere-src-5.15.1/configure -platform linux-rpi4-v3d-g++ -v -opengl es2 -eglfs -no-gtk -no-xcb -opensource -confirm-license -release -reduce-exports -force-pkg-config -nomake examples -no-compile-examples -skip qtwayland -skip qtwebengine -skip qt3d -skip qtlocation -skip qtscript -skip qtsensors -skip qtserialport -skip qtspeech -skip qtcharts -skip qtvirtualkeyboard -skip qtquick3d  -qt-pcre -no-pch -ssl -evdev -system-freetype -fontconfig -glib -prefix /opt/Qt5.15 -qpa eglfs
+```
+
+And build it!
+```bash
+make -j4
+sudo make install
+```
+
+### Notes
+It is recommended to use swap - at least 1 GB. 
+It is also recommended to use `tmux` for running the build for cases of SSH disconnections.
+You should also cool the Raspberry Pi properly, a small fan is enough to lower the CPU temperature by 20 C!.