Document adding website docs for datasources in more detail

[rileykarson]

Background

We have a lot of datasources that predate the datasource wrapper, and what I'd call "modern" datasource docs like those for https://registry.terraform.io/providers/hashicorp/google/latest/docs/data-sources/compute_backend_bucket. I've seen a few contributions that have documented individual resource fields, for example- we should make it clear in our contribution guide the exact formatting we're looking for, probably by linking to an example like the backend bucket page. It's currently a single list entry, "Add documentation": https://github.com/GoogleCloudPlatform/magic-modules/blob/main/mmv1/third_party/terraform/README.md#datasource

What kind of contribution is this issue about?

datasources

Related PR(s), if any:

Details