docs: update local-development.mdx

[Amit1712]

In this page it says to use the project_slug https://www.ory.sh/docs/cli/ory-tunnel When I used the project id I encountered weird problems ('Invalid hostname') returned from get-flow sdk function call

Related Issue or Design Document

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact security@ory.sh) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

Further comments

[CLAassistant]

All committers have signed the CLA.

[vinckr]

Thanks a lot, I missed that one!

One small change then we can merge 🙏