Improve documentation on installation procedure

[945fc41467]

Hello,

I had to compile it several times to find how to have a full functional rtklib distribution. Maybe the documentation could be more exhaustive and give the full list of commands at least for main distributions. For example in Ubuntu LTS, with QT5:

# Install dependencies. (name of packet are slightly different for Qt6):
sudo apt install qtbase5-dev
sudo apt install qttools5-dev
sudo apt install libqt5xmlpatterns5-dev
sudo apt install ribqt5serialport5-dev
sudo apt install qtwebengine5-dev
# Compile sources:
cd .local/share  # Not sure if this is the cleanest place to put it. But this ok enough for me.
git clone https://github.com/rtklibexplorer/RTKLIB.git
cd RTKLIB
mkdir build
cd build
cmake ..
make
make test
# Installation in users directory. Maybe a symbolic link would have been cleanest:
cp ../bin/* $HOME/.local/bin
cp ../app/qtapp/icon/* $HOME/.local/share/icons
cp ../app/qtapp/*/*.desktop $HOME/.local/share/applications

This would have make me save a lot of time.

Thanks.