ReadMe correction

[rmiryala]

git clone https://github.com/AVSystem/Anjay.git
cd Anjay
docker build --tag anjay .

The above one yields error
I guess it has to be in the following way
git clone https://github.com/AVSystem/Anjay.git
cd Anjay
git submodule update --init
docker build --tag anjay .

[Mateusz Krawiec]

Thank you for the report! We've updated README.md accordingly in 2.4.3.