how to push an image to docker hub?
horribly insecure:
root $ 
root $ docker login
Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com to create one.
Username: nicksaunders
Password: 
WARNING! Your password will be stored unencrypted in /root/snap/docker/471/.docker/config.json.
Configure a credential helper to remove this warning. See
https://docs.docker.com/engine/reference/commandline/login/#credentials-store

Login Succeeded
root $ 
root $ docker images
REPOSITORY                   TAG                 IMAGE ID            CREATED             SIZE
helloworld_web               latest              3118807ab0e0        13 minutes ago      196MB
frappe/erpnext-nginx         latest              e417869e11ba        39 hours ago        414MB
frappe/erpnext-worker        latest              96559438dfec        40 hours ago        1.22GB
frappe/frappe-nginx          latest              3d006c375c6e        40 hours ago        410MB
frappe/frappe-worker         latest              961988528953        40 hours ago        1GB
frappe/frappe-socketio       latest              bca49f1b4a04        40 hours ago        180MB
frappe/bench                 latest              8c1bc9d3a572        40 hours ago        1.4GB
frappe/erpnext-docs-nginx    latest              7d117e2bd798        42 hours ago        428MB
frappe/erpnext-docs-worker   latest              a1c0b0511e92        42 hours ago        2.88GB
frappe/erpnext-worker        &lt;none&gt;              09be9dde8f8f        2 days ago          1.21GB
frappe/bench                 &lt;none&gt;              c775a49dee59        2 days ago          1.4GB
redis                        alpine              bd71e6db4a54        13 days ago         32.2MB
python                       3.7-alpine          295b051ee125        2 weeks ago         41.7MB
basex/basexhttp              latest              3339bf6bc898        3 weeks ago         226MB
twilio/twilio-java           latest              611ab7ece1cf        5 weeks ago         993MB
mysql                        latest              0d64f46acfd1        7 weeks ago         544MB
jetty                        latest              5f997007f18d        7 weeks ago         522MB
jitsi/web                    latest              1fad75476320        2 months ago        483MB
mysql/mysql-server           latest              8a3a24ad33be        2 months ago        366MB
hello-world                  latest              bf756fb1ae65        8 months ago        13.3kB
lukptr/erpnext7              latest              130f3d9f222f        14 months ago       3.59GB
root $ 
root $ docker tag helloworld_web nicksaunders/helloworld:firsttry
root $ 
root $ docker push nicksaunders/helloworld
The push refers to repository [docker.io/nicksaunders/helloworld]
fca41575e369: Pushed 
40f0977ea685: Pushing [==================================================&gt;]  12.08MB
f8b013a4d861: Pushed 
1d6d0bace1b8: Pushing [====&gt;                                              ]  13.03MB/143MB
aabee2d268fc: Pushed 
22ee430ae506: Waiting 
60faa6c61cf9: Waiting 
cfd52085ef94: Waiting 
408e53c5e3b2: Waiting 
50644c29ef5a: Waiting 

but seems to work.