docs: Add note regarding HCP workers (#3514)

* docs: Add note regarding HCP workers

* docs: Make parameter link

* docs: Reword and move `hcp_boundary_cluster_id`

website/content/docs/configuration/worker/index.mdx

@@ -74,6 +74,14 @@ worker {
   using env or file, their contents must formatted as a JSON array:
   `["127.0.0.1", "192.168.0.1", "10.0.0.1"]`
 
+  HCP Boundary workers require the [`hcp_boundary_cluster_id`](/boundary/docs/configuration/worker/#hcp_boundary_cluster_id) parameter instead of `initial upstreams`.
+  If you configure an HCP worker with `initial_upstreams`, the worker configuration fails.
+
+- `hcp_boundary_cluster_id` - A string that you must use to configure PKI workers
+  to connect to your HCP Boundary cluster rather than specifying
+  `initial_upstreams`. This parameter is currently only valid for workers using the PKI
+  registration method and for workers directly connected to HCP Boundary.
+
 - `tags` - A map of key-value pairs where values are an array of strings. Most
   commonly used for [filtering](/boundary/docs/concepts/filtering) targets a
   worker can proxy via [worker
@@ -81,11 +89,6 @@ worker {
   set here will be re-parsed and new values used. It can also be a string
   referring to a file on disk (`file://`) or an env var (`env://`).
 
-- `hcp_boundary_cluster_id` - A string that can be used to configure PKI workers
-  to connect to your HCP Boundary cluster rather than specifying
-  `initial_upstreams`. This is currently only valid for workers using the PKI
-  registration method and for workers directly connected to HCP Boundary.
-
 ## Signals
 
 The `SIGHUP` signal causes a worker to reload its configuration file to pick up any updates for the `initial_upstreams` and `tags` values.