add requirements.txt file or something other allowing automatic install of python dependencies

[matkoniecz]

I tried again to try fixing some of bugs that I reported (#577 etc) but got stuck on installing (maybe I should send an untested PR instead...).

Is there already a way to setup at least python dependencies automatically?

pip3 install --user -r requirements.txt seems quite standard way, and right now https://github.com/EdwardBetts/osm-wikidata/blob/master/INSTALL#L13 seems to recommend a manual install.

Would you accept PR adding requirements.txt file or is there already something fullfilling this functionality that needs to be mentioned in INSTALL file?

[matkoniecz]

Is there chance of something appearing? I would gladly make PR for issues that I keep opening (and block reasonable use of this tool in my area), but right now there is no sane way to do this.