Add docs

Author: tptee

website/docs/r/service_github.html.markdown

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+---
+layout: "gitlab"
+page_title: "GitLab: gitlab_service_github"
+sidebar_current: "docs-gitlab-resource-service_github"
+description: |-
+  Manage GitHub integration that updates pipeline statuses on a GitHub repo's pull requests.
+---
+
+# gitlab\_service\_github
+
+**NOTE**: requires either EE (self-hosted) or Silver and above (GitLab.com).
+
+This resource manages a [GitHub integration](https://docs.gitlab.com/ee/user/project/integrations/github.html) that updates pipeline statuses on a GitHub repo's pull requests.
+
+## Example Usage
+
+```hcl
+resource "gitlab_project" "awesome_project" {
+  name = "awesome_project"
+  description = "My awesome project."
+  visibility_level = "public"
+}
+
+resource "gitlab_service_github" "github" {
+  project        = "${gitlab_project.awesome_project.id}"
+  token          = "REDACTED"
+  repository_url = "https://github.com/terraform-providers/terraform-provider-gitlab"
+}
+```
+
+## Argument Reference
+
+The following arguments are supported:
+
+* `project` - (Required) ID of the project you want to activate integration on.
+
+* `repository_url` - (Required) The URL of the GitHub repo to integrate with, e,g, https://github.com/terraform-providers/terraform-provider-gitlab.
+
+* `token` - (Required) A GitHub personal access token with at least `repo:status` scope.
+
+* `static_context` - (Optional) Append instance name instead of branch to the status. Must enable to set a GitLab status check as _required_ in GitHub. See [Static / dynamic status check names] to learn more. 
+
+## Importing GitHub service
+
+ You can import a service_github state using `terraform import <resource> <project_id>`:
+
+```bash
+$ terraform import gitlab_service_github.github 1
+```