docs: add host set documentation

website/docs/r/resource_host_set.html.markdown

@@ -0,0 +1,62 @@
+---
+layout: "boundary"
+page_title: "Boundary: hostset_resource"
+sidebar_current: "docs-boundary-hostset-catalog-resource"
+description: |-
+  Hostset resource for the Boundary Terraform provider.
+---
+
+# host_set_resource 
+The host_set resource allows you to configure a Boundary host set. Host sets are
+always part of a host catalog, so a host catalog resource should be used inline
+or you should have the host catalog ID in hand to successfully configure a host
+set. 
+
+## Example Usage
+
+```hcl
+resource "boundary_organization" "foo" {}
+
+resource "boundary_project" "example" {
+  description = "My first project!"
+  scope_id    = boundary_organization.foo.id
+}
+
+resource "boundary_host_catalog" "static" {
+  scope_id = boundary_project.example.id
+}
+
+resource "boundary_host" "1" {
+  name            = "host_1"
+  description     = "My first host!"
+  address         = "10.0.0.1:8080"
+  host_catalog_id = boundary_host_catalog.static.id
+  scope_id        = boundary_project.example.id
+}
+
+resource "boundary_host" "2" {
+  name            = "host_2"
+  description     = "My second host!"
+  address         = "10.0.0.2:8080"
+  host_catalog_id = boundary_host_catalog.static.id
+  scope_id        = boundary_project.example.id
+}
+
+resource "boundary_host_set" "web" {
+  host_catalog_id = boundary_host_catalog.static.id
+  host_ids        = [
+    boundary_host.1.id,
+    boundary_host.2.id,
+  ]
+}
+```
+
+## Argument Reference
+
+The following arguments are required:
+* `host_catalog_id`- The catalog for the hostset.
+
+The following arguments are optional:
+* `name` - The hostset name. Defaults to the resource name.
+* `description` - The hostset description.
+* `host_ids` - The list of host IDs contained in this set.