website: github_team_repository purpose clarification

With the addition of github_repository it may be confusing that
github_team_repository only creates relationships, rather than creating
actual repositories. To reduce the chance of confusion, we'll make this
explicit in the docs for github_team_repository.

Also taking this opportunity to make the examples consistent with what
would be produced by hclfmt.

website/source/docs/providers/github/r/team_repository.html.markdown

@@ -3,29 +3,38 @@ layout: "github"
 page_title: "GitHub: github_team_repository"
 sidebar_current: "docs-github-resource-team-repository"
 description: |-
-  Provides a GitHub team repository resource.
+  Manages the associations between teams and repositories.
 ---
 
 # github\_team_repository
 
-Provides a GitHub team repository resource.
+This resource manages relationships between teams and repositories
+in your Github organization.
 
-This resource allows you to add/remove repositories from teams in your organization. When applied,
-the repository will be added to the team. When destroyed, the repository will be removed from the team.
+Creating this resource grants a particular team permissions on a
+particular repository.
+
+The repository and the team must both belong to the same organization
+on Github. This resource does not actually *create* any repositories;
+to do that, see [`github_repository`](repository.html).
 
 ## Example Usage
 
 ```
 # Add a repository to the team
 resource "github_team" "some_team" {
-    name = "SomeTeam"
-    description = "Some cool team"
+  name        = "SomeTeam"
+  description = "Some cool team"
+}
+
+resource "github_repository" "some_repo" {
+  name = "some-repo"
 }
 
 resource "github_team_repository" "some_team_repo" {
-	team_id = "${github_team.some_team.id}"
-	repository = "our-repo"
-	permission = "pull"
+  team_id    = "${github_team.some_team.id}"
+  repository = "${github_repository.some_repo.name}"
+  permission = "pull"
 }
 ```
 
@@ -35,5 +44,5 @@ The following arguments are supported:
 
 * `team_id` - (Required) The GitHub team id
 * `repository` - (Required) The repository to add to the team.
-* `permission` - (Optional) The permissions of team members regarding the repository. 
-                  Must be one of `pull`, `push`, or `admin`. Defaults to `pull`.
+* `permission` - (Optional) The permissions of team members regarding the repository.
+  Must be one of `pull`, `push`, or `admin`. Defaults to `pull`.