update dockerfiles to build 2.1 better, and also give a hint to push the latest

docker/Dockerfile

-# Dockerfile for binary_c (2.30pre32) and binary_grid2
+# Dockerfile for binary_c (2.1) and binary_grid2
 # based on Ubuntu 18.04
 
 FROM ubuntu:18.04

docker/build.sh

@@ -65,8 +65,16 @@ docker tag binary_c robizzard/binary_c:latest
 ############################################################
 # now you should do "docker push robizzard/binary_c:master<version>
 ############################################################
-echo "Now you should run:"
+echo "Now you should"
+echo
+echo "Run the following command to update tagged version $BINARY_C_VERSION"
+echo
 echo "docker push robizzard/binary_c:master$BINARY_C_VERSION"
+echo
+echo "Run the following command to then update the latest tag"
+echo
+echo "docker push robizzard/binary_c"
+echo
 
 ############################################################
 # clean up the temporary directory

docker/run.sh

@@ -37,7 +37,7 @@ docker run \
        -v /tmp/.X11-unix \
        -v $XAUTH \
        -v $HOME/.Xauthority:/home/binary_c/.Xauthority \
-       robizzard/binary_c:master2.0pre32 \
+       robizzard/binary_c:latest \
        /bin/bash -c "sudo chown binary_c binary_c_persistent ; sudo chgrp binary_c binary_c_persistent; cat /home/binary_c/progs/stars/binary_c/doc/README.docker; bash --login"