Update README.md, autograder/Dockerfile files

README.md

-# simavr-ci-test
+# Simavr Environment
 
+This repository contains [docker](https://www.docker.com/get-started) images that contain ubuntu linux with [compilers](https://www.geeksforgeeks.org/gcc-command-in-linux-with-examples/) and [simavr](https://github.com/buserror/simavr) simulator to help one test embedded C code without an actual device.
+
+## Usage
+
+No planned usage directly, but you can

autograder/Dockerfile

@@ -25,7 +25,7 @@ RUN apt-get update && \
   sudo \
   && ln -fs /usr/share/zoneinfo/Europe/Helsinki /etc/localtime \
   && DEBIAN_FRONTEND="noninteractive" dpkg-reconfigure --frontend noninteractive tzdata \
-  rm -rf /var/lib/apt/lists/*
+  && rm -rf /var/lib/apt/lists/*
 
 # Install autodriver
 WORKDIR /home