clarify that the provider source needs to be specified

[afeld]

Test Plan

• Try creating a Terraform root module with only the provider, no source — terraform init fails with Could not retrieve the list of available versions for provider hashicorp/snowflake: provider registry registry.terraform.io does not have a provider named registry.terraform.io/hashicorp/snowflake

  provider "snowflake" {}

• Try creating a Terraform root module with a source — terraform init succeeds

  terraform {
    required_providers {
      snowflake = {
        source = "Snowflake-Labs/snowflake"
      }
    }
  }
  
  provider "snowflake" {}

References

• https://developer.hashicorp.com/terraform/language/providers/requirements#source-addresses

[sfc-gh-jcieslak]

Hey @afeld 👋
As we were making bigger changes to the documentation we added your suggestion as part of the #2931 pr. We couldn't merge this, because you changed the generated markdown which would be overridden in the next change.
Nevertheless, Thank You for your contribution, we really appreciate it!