Use v1 contributing info on main porter site

[carolynvs]

What does this change

Now that all new development should be against the release/v1 branch, I've updated the contributing tutorial on the main branch to instruct people to work with release/v1 and use the udpated v1 instructions.

We have been getting a number of confused contributors because they come to the contributing tutorial from the main site which is for our main branch and this should help get them the correct info to contribute.

Here is a preview of the updated contributing tutorial https://deploy-preview-2173--porter.netlify.app/contribute/tutorial/

What issue does it fix

Closes #2172

Notes for the reviewer

I will open a follow-up PR to the v1 branch with some of the other tweaks I made to the contributing tutorial so that they are both up-to-date.

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR