Workflow 16 feature docs

[nathanwoulfe]

📋 Description

Adds feature documentation for Alternate Versions and Release Sets, both new in Workflow 16.

✅ Contributor Checklist

I've followed the Umbraco Documentation Style Guide and can confirm that:

• Code blocks are correctly formatted.
• Sentences are short and clear (preferably under 25 words).
• Passive voice and first-person language (“we”, “I”) are avoided.
• Relevant pages are linked.
• All links work and point to the correct resources.
• Screenshots or diagrams are included if useful.
• Any code examples or instructions have been tested.
• Typos, broken links, and broken images are fixed.

Product & Version (if relevant)

Umbraco Workflow 16.0.0

Deadline (if relevant)

June 12-ish

[nathanwoulfe]

Hey @eshanrnh I've tagged you into this one if you'd like to cast an expert eye over my additions. I think both features can be further documented in future, but as a getting-started guide for each, this should be ok.

It all makes sense to me - as it should, given I built it all - but please let me know if anything needs more context or explanation.

[eshanrnh]

The PR looks great, @nathanwoulfe 🙌 I think you have covered everything that's required 💪 I have a few suggestions based on the styleguide, typos, missing periods and so on which I'll incrorporate 😊