Add some basic run instructions (comments) in the Dockerfile

Dockerfile

@@ -4,3 +4,7 @@ WORKDIR /usr/src
 COPY requirements.txt ./
 RUN pip install --no-cache-dir -r requirements.txt
 RUN git clone --depth 1 https://github.com/StevenBlack/hosts.git
+
+# Now you launch this with
+#  $ docker build ./
+#  $ docker run -it (containerid) bash