Add wiki contribution guidance

Contributing-to-the-Wiki.md

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+# Contributing to the Wiki
+
+Help make this a useful player guide. Good first contributions include a tested crafting walkthrough, a screenshot showing a workstation step, a clearer explanation of a Page, or a correction to instructions that changed in a new release.
+
+1. Check the [current implementation](https://git.paddedcell.org/dnorberg/rivencraft/src/branch/main/docs/CURRENT_IMPLEMENTATION.md) and the latest [release](https://git.paddedcell.org/dnorberg/rivencraft/releases) before documenting a feature.
+2. Edit an existing wiki page if you have access, or [open an issue](https://git.paddedcell.org/dnorberg/rivencraft/issues) with proposed wording and your tested game/mod versions.
+3. Keep player instructions distinct from OP-only commands and optional integrations. Call out behavior that differs between a handheld book, Book Stand, and portal.
+4. Use original screenshots where possible. Credit outside material and do not paste copyrighted guide text without permission. Remove usernames, tokens, server addresses, and private world data from screenshots and logs.
+
+Rivencraft is inspired by **Mystcraft**, created by **XCompWiz**. Please keep that credit visible when reusing Legacy information. The [original Mystcraft](https://www.curseforge.com/minecraft/mc-mods/mystcraft), [unfinished Mystcraft 2](https://www.curseforge.com/minecraft/mc-mods/mystcraft-2), [Rivencraft NOTICE](https://git.paddedcell.org/dnorberg/rivencraft/src/branch/main/NOTICE), and [asset provenance](https://git.paddedcell.org/dnorberg/rivencraft/src/branch/main/docs/ASSET_PROVENANCE.md) are the starting points for attribution.