Add Dockerfile for building within a container

.dockerignore

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+add_emoji_gsub.pyc
+build
+waveflag
+
+.git/

Dockerfile

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+FROM python:buster
+RUN apt update && apt install -y \
+    git \
+    zopfli \
+    libcairo2-dev
+
+# Install nototools
+RUN git clone https://github.com/googlefonts/nototools.git /nototools
+WORKDIR /nototools
+RUN pip install -r requirements.txt
+RUN pip install -e .
+
+ADD . /blobmoji
+WORKDIR /blobmoji
+
+# Build blobmoji font
+CMD make -j $(nproc)