update docs to use --alias

[edublancas]

the intro guide: https://jupysql.ploomber.io/en/latest/intro.html#assignment

still shows the old way to switch connections via user@db (%%sql will@shakes)

we should update this to use the new --alias feature: https://jupysql.ploomber.io/en/latest/howto.html#switch-connections

[tl3119]

I have updated the document and submitted a pull request. Please check!

[edublancas]

can you share the link to the PR? I cannot find it

[tl3119]

The PR is the same with #561 this one. Sorry, I don't know why it automatically goes to the same PR after I push it. How should I separate them?

[edublancas]

you need to create separate branches, then open PRs from those separate branches

[tl3119]

you need to create separate branches, then open PRs from those separate branches

Please check here: #574

[edublancas]

fixed by #574