Update documentation

[jbelien]

Following the restructure (f157bfb), the documentation needs to be updated/fixed !

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• Finish geojson.php script documentation
• Write statistics.php script documentation

[mitmirzutun]

I cloned the repository with the git clone command (git clone https://github.com/openknowledgebe/equalstreetnames.git) in the documentation to run on my computer and it didn't clone the submodules.
It cloned correctly with git submodule init followed by git submodule update --recursive within the cloned directory (taken from git-scm.com/docs/git-submodule) or clone everything with git clone --recursive https://github.com/openknowledgebe/equalstreetnames.git

[jbelien]

Hello @mitmirzutun, indeed, each city is a sub-module !
You can find all documentation on how to work with sub-modules here: https://git-scm.com/book/en/v2/Git-Tools-Submodules.