Create get started -documentation for developers

[rioksane]

Create step by step instructions on how to build up the plone.org site locally with the theme. This is needed so that new developers could easily help with theming issues.

[stevepiercy]

@rioksane can this issue be closed, per https://github.com/plone/plone.org?tab=readme-ov-file#quick-start?

[rioksane]

Yes, issue can be closed

[stevepiercy]

The current readme is incorrect. I created a PR awaiting review at #248