Move wiki from docs to gdext

[panno8M]

We've enabled to install the entire library via nimble install https://.../gdext. So it would be more convenient to refer wiki if we move that from docs to gdext.

You may do this while updating the wiki. Please do so when you have time.

[insomniacUNDERSCORElemon]

To be clear, you intend to remove the .docs repo then, once the wiki is moved? I believe you need to enable wiki in repo settings (like you did for .docs) if so, as I'm not sure if settings can be changed via normal PRs.

Though honestly, I don't currently have a lot of ideas for solid wiki changes* right now. I need to try other things, as I've said. This combined with my lack of usage of Github means I can't make promises (at least with any known date), though I say that in the current moment.

Is gdext new landing page for the project? If so, maybe gdext-nim would be a better name for name recognition (I know this is redundant internally, but gdext on its own just sounds like a nickname for GDextension). Also further context about Godot versioning (4.0+, 4.2, 4.X etc) on that repo might help too**, as I expect most users would use those search terms rather than GDextension.

*= All my current thoughts:

• a blank home page probably isn't useful
• also, 'running demo' page seems a bit redundant with readme files
  • especially an issue if users visit demos first
  • difference in exact instructions, needing to understand structure to build w/general instruction
• is embedding wiki pages a thing? It might make more sense right now
  • individual pages as sections still, but instead they are merged into one page just for viewing
  • collated I guess would be to correct term, easier for multiple people to edit as collation is separate
• usage info, such as node type stuff, but that's all I have now
  • and the demos probably make that one clear already

**= I know you do this on the org page, but aside from higher search results for landing page the org page should also explicitly point to the landing repo.