Edit Dockerfile to run python script

Add configuration description

Dockerfile.template

@@ -7,11 +7,6 @@ ENV INITSYSTEM on
 ENV RESIN_ARCH %%RESIN_ARCH%%
 ENV RESIN_MACHINE_NAME %%RESIN_MACHINE_NAME%%
 
-# Version number of gateway software.
-# (Incrementing this simply forces Docker to flush its cache
-#  and thus forces a full rebuild. Not used outside of Dockerfile.)
-ENV TTN_GATEWAY_SOFTWARE 51
-
 # Copy the build and run environment
 COPY . /opt/ttn-gateway/
 WORKDIR /opt/ttn-gateway/
@@ -20,4 +15,4 @@ WORKDIR /opt/ttn-gateway/
 RUN ./dev/build.sh && rm -rf ./dev
 
 # Start it up
-CMD ["sh", "-c", "./run.sh"]
+CMD ["sh", "-c", "./run.py"]