added Dockerfile (fixes #17)

Dockerfile

@@ -0,0 +1,17 @@
+FROM library/php:7.1.31-alpine
+
+RUN apk add --update git zip && \
+    adduser --no-create-home -S --disabled-password --shell /bin/sh php
+
+COPY . /src
+
+WORKDIR /src
+
+RUN curl --silent --show-error https://getcomposer.org/installer | php
+
+RUN php composer.phar install && \
+    cp .env.example .env
+
+USER php
+
+CMD ["php", "artisan", "serve"]