Docs: Update login command in the prerequisites page

[zameel7]

learn-graphql/tutorials/backend/hasura-v3/tutorial-site/content/setup.md

Line 29 in 5e19739

ddn login

Here, it suggests to run the command ddn login but seems like the actual command to be run is ddn auth login

[zameel7]

Seems like the docs are fully yet to be modified.