Fix errors in documents

Description: I noticed a few issues and inconsistencies in the installation and setup documentation. Correcting these will help new contributors and users set up the project smoothly.

Issues Found : Admin user creation command : Current : python manage.py dosuperuser Correct : python manage.py createsuperuser

 Database dump command :
       Current : pg_dump dbname=ecommerce -f /tmp/ecommerce.psql
       Correc t: pg_dump -U postgres -d ecommerce -f /tmp/ecommerce.psql

 Elastic Search version not specified :
       Currently says : "install Elastic Search (use brew)"
       Suggestion : Specify supported version e.g Elasticsearch 7.x