Add basic Docker setup

After cloning, simply:
```sh
docker-compose build
docker-compose run --rm mongoengine python setup.py test
```

Author: juannyG

Dockerfile

@@ -0,0 +1,9 @@
+FROM python:3.8-slim-buster AS build
+
+COPY requirements-dev.txt .
+RUN pip install --upgrade pip
+RUN pip install -r requirements-dev.txt
+RUN pip install "pymongo>=3.4,<4.0"
+
+WORKDIR /app
+COPY . ./

docker-compose.yml

@@ -0,0 +1,17 @@
+version: '3.4'
+services:
+  mongoengine:
+    build:
+      context: .
+    image: mongoengine:latest
+    network_mode: host
+    depends_on:
+      - mongo
+    working_dir: /app
+    volumes:
+      - .:/app
+  mongo:
+    image: mongo:4
+    restart: always
+    ports:
+      - 27017:27017