Add note about LightmapGI only baking nodes under its parent

[FlooferLand]

LightmapGI's documentation currently doesn't mention the fact it only bakes nodes under its parent.
This can make the user think there is something wrong with their scene setup or 3D models, as it refuses to bake when the user's models / world isn't under the same parent as the LightmapGI.

I personally encountered this issue because I tried adding a LightmapGI underneath a blank node called "Environment" under which a WorldEnvironment was also present, and the LightmapGI complained about having nothing to bake.

Made for the godotengine/godot-docs#9694 issue
Linked PR: godotengine/godot-docs#10247

[jcostello]

Meshes or its the same for lights?

[mhilbrunner]

LGTM. Just merged the corresponding docs repo PR.

[FlooferLand]

@jcostello Meshes or its the same for lights?

Sorry for the very late reply!
The LightmapGI node only looks at nodes underneath its parent, its the same for all types.
I believe this was done so you could have several separate lightmaps in the same scene (which is neat!)

For a more in-depth explanation:
The editor calls the bake function via _bake_select_file and provides either the LightmapGI or the LightmapGI's parent as the node to scan from. The bake function then calls _find_meshes_and_lights which is a recursive function that gets all the children of the node thats passed into it

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉