copied and pasted the following code changing the email and password. To the one I put in when prompted for and while running command line sudo apt-get install pgadmin4 apache.
ran sudo docker sudo docker run -p 80:80 -e 'PGADMIN_DEFAULT_EMAIL=zahidr1000@gmail.com' -e 'PGADMIN_DEFAULT_PASSWORD=*******' -d dpage/pgadmin4
Here is the KICKER. (not http://127.0.0.1/pgadmin4) go to browser and type http://127.0.0.1 and you will see the blue login screen prompting you for the above email and password.
That's certainly how you can deploy a pgAdmin container. Unless you specifically want to use the container though, I would use the Debian/Ubuntu packages, per the article you linked to above. We don't maintain those directly though, so I'm not sure how accurate those instructions are. It would probably help if you posted error messages etc.