Add a simple dockerfile

Tested well enough on Windows, but minimal confidence in it continuing to work. 

Fixes https://github.com/matrix-org/pantalaimon/issues/13

The patch mentioned in the issue doesn't seem to be needed anymore.

Dockerfile

@@ -0,0 +1,18 @@
+FROM python:3.7-slim-stretch
+
+# Many of these dependencies are required to build the app's dependencies, so staging these out doesn't help much
+RUN mkdir -p /app
+RUN apt-get update && apt-get install -y git gcc clang cmake pkg-config libdbus-1-dev libglib2.0-dev libcairo2-dev python3-dev libgirepository1.0-dev wget
+
+WORKDIR /app
+RUN wget https://gitlab.matrix.org/matrix-org/olm/-/archive/master/olm-master.tar.bz2 \
+    && tar -xvf olm-master.tar.bz2 \
+    && cd olm-master && make && make PREFIX="/usr" install && cd ../ \
+    && rm -r olm-master
+
+COPY . /app
+RUN pip install . gobject PyGObject "matrix-nio@git+https://github.com/poljar/matrix-nio.git@dev#egg=matrix-nio-0" && python setup.py install
+
+VOLUME /data
+ENTRYPOINT ["pantalaimon"]
+CMD ["-c", "/data/pantalaimon.conf"]

README.md

@@ -67,6 +67,30 @@ cd notification-daemon-mac-py
 ./notify.py
 ```
 
+### Docker
+
+An experimental Docker image can be built for Pantalaimon, primarily for use in bots.
+
+```bash
+docker build -t pantalaimon .
+# Create a pantalaimon.conf before running. The directory mentioned in the
+# volume below is for where Pantalaimon should dump some data.
+docker run -it --rm -v /path/to/pantalaimon/dir:/data -p 8008:8008 pantalaimon
+```
+
+An example `pantalaimon.conf` for Docker is:
+```conf
+[Default]
+LogLevel = Debug
+SSL = True
+
+[local-matrix]
+Homeserver = https://matrix.org
+ListenAddress = 0.0.0.0
+ListenPort = 8008
+SSL = False
+```
+
 ### Experimental E2E search support.
 
 Pantalaimon can handle the search endpoint of a Matrix server as well, providing