Use instancing example from godot-projects for the "Step by step: Instancing" page

[rm-code]

As discussed in PRs #6187 and #5374 the instancing demo from the "Step by step" tutorials could be moved to the godot-demo-projects repository for v4.

But I think it would make more sense to reuse the already existing (and nearly identical) instancing project:
https://github.com/godotengine/godot-demo-projects/tree/master/2d/instancing

I would be up for a PR to rewrite the necessary parts of the docs and add new screenshots, but I'm not sure how we would handle this going forward. E.g. how can we link to a specific version of a demo-project?

[Calinou]

E.g. how can we link to a specific version of a demo-project?

You can link to a tagged release once such a tag is is made for 4.0.

GitHub doesn't allow downloading a single folder of a repository as a ZIP, but this can be done with external services (source).

[rm-code]

@Calinou I added a note about the download-service which could be removed later on.

[wirecat]

@rm-code What if we had someone cut a release of godotengine/godot-demo-projects for the 4.0 tag? Then there would be generated zips that docs could reference. It's pretty convenient as a user to be able to just download the zip and go.

The downside is any subsequent 4.0 releases would result in docs needing to update links to point at the new release. Pointing at the 4.0 branch like you're doing avoids that which is nice.

Example of previous release: https://github.com/godotengine/godot-demo-projects/releases/tag/3.5-9e68af3

e: I also wanted to say thank you for working on this! I was just working through docs and hit the current zip that doesn't work in Godot 4 without a small amount of massaging.

[rm-code]

@wirecat The original idea was to link to the asset store which in turn references the release tag you mentioned:

I added the note in the PR to allow a quick merge, instead of having to wait for the asset store to update.

I also wanted to say thank you for working on this! I was just working through docs and hit the current zip that doesn't work in Godot 4 without a small amount of massaging.

I'm a beginner with Godot as well and just wanted to help where I can :D