Update doc: add project_shared_with_groups option

Author: Jordan Caussat

website/docs/r/project.html.markdown

@@ -50,6 +50,11 @@ The following arguments are supported:
   Valid values are `private`, `internal`, `public`.
   Repositories are created as private by default.
 
+* `shared_with_groups` - (Optional) Enable sharing the project with a list of groups (maps).
+  * `group_id` - (Required) Group id of the group you want to share the project with.
+  * `group_access_level` - (Optional) Group's sharing permissions. See [group members permission][group_members_permissions] for more info.
+  Valid values are `guest`, `reporter`, `developer`, `master`.
+
 ## Attributes Reference
 
 The following additional attributes are exported:
@@ -66,6 +71,9 @@ The following additional attributes are exported:
 
 * `runners_token` - Registration token to use during runner setup.
 
+* `shared_with_groups` - List of the groups the project is shared with.
+  * `group_name` - Group's name.
+
 ## Importing projects
 
 You can import a project state using `terraform import <resource> <id>`.  The
@@ -75,3 +83,4 @@ its `:id` value, so for example:
     terraform import gitlab_project.example richardc/example
 
 [get_single_project]: https://docs.gitlab.com/ee/api/projects.html#get-single-project
+[group_members_permissions]: https://docs.gitlab.com/ce/user/permissions.html#group-members-permissions