Explain how to switch to add native namespace

[gforcada]

To go along with the plone/Products.CMFPlone#3928

Disclaimer: I have no idea where would be the best place to put this documentation within the structure, and probably the admonitions style is not the right one.

We can polish, but before nitpicking on this details, let's agree on the structure of the document and if it explains all the relevant steps and are clear enough.

Once that's done we can do the polish.

@mauritsvanrees @davisagli: given a random Plone contributor, do you think the steps cover all the steps, and are clear enough? I made it generic enough (with tips to skip sections) so that it can be reused for collective or private packages, where we can not convert all ourselves.

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📚 Documentation preview 📚: https://plone6--1981.org.readthedocs.build/

[stevepiercy]

@gforcada this is a how-to guide for developers, so it belongs in docs/developer-guide with a toctree entry in docs/developer-guide/index. Would you please move it there?

I'll do a thorough non-technical review after the technical structure and details are reviewed and approved.

Thank you!

[mauritsvanrees]

Overall good, but I made some suggestions.

[gforcada]

@mauritsvanrees thanks for all the tips and improvements! 🙇🏾 that's much better ✨

@stevepiercy I moved the file to the location you suggested and add a ToC entry.

Now is probably the time to improve the wording, which probably needs plenty 😅

[stevepiercy]

@gforcada I requested another review from @mauritsvanrees, and I'd like @davisagli to review as well, before I make my final pass for non-technical stuff.