Added Dockerfile

[ThatXliner]

Dockerfiles make it easy for people who can't/didn't install FontForge on their computer (like me) but instead have docker.

To use this docker file, edit the build.py, build the docker image with docker build . -t ligaturizer and run it like so:

docker run --name ligma ligaturizer
mkdir container
docker export ligma > container/container.tar
cd container
tar xf container.tar
cp -r Ligaturizer/fonts/output ../fonts
cd ..
rm -rf container
docker rm ligma

What this does is generate the fonts and put them in the fonts/output folder

[astrolemonade]

You should have a look at my PR for nerd-fonts: ryanoasis/nerd-fonts#684
You should use alpine instead of ubuntu since it is a lot smaller.