Dockerfile: Made the resulting image more friendly by using ENTRYPOINT

Dockerfile

@@ -25,4 +25,5 @@ RUN apk update --no-cache && \
 COPY --from=cmatrixbuildimage /cmatrix/cmatrix /cmatrix
 
 USER cmatrix
-CMD ["./cmatrix"]
+ENTRYPOINT ["./cmatrix"]
+CMD ["-akb", "-u 3"]