fix: revert README changes, shorten variable description

Move migration docs to public Ona documentation instead of the
module README. Shorten the variable description to one sentence.

Co-authored-by: Ona <no-reply@ona.com>

Author: nandajavarma

README.md

@@ -26,47 +26,6 @@ for setup instructions, configuration options, and troubleshooting.
 The [`runner-with-networking`](./examples/runner-with-networking/) example
 provides a full infrastructure setup including VPC, DNS, and certificates.
 
-## Project Metadata Mode
-
-By default this module uses `google_compute_project_metadata` (authoritative),
-which manages **all** project-level metadata. Any metadata keys not declared in
-this module will be removed on `terraform apply`.
-
-If other systems or Terraform modules manage project metadata in the same GCP
-project, set `use_authoritative_project_metadata = false` to switch to per-key
-`google_compute_project_metadata_item` resources. This only manages the keys
-the module needs (`enable-oslogin`, `gitpod-runner-id`) and leaves everything
-else untouched.
-
-```hcl
-module "runner" {
-  source = "gitpod-io/ona-runner/google"
-  # ...
-  use_authoritative_project_metadata = false
-}
-```
-
-### Migrating an existing deployment to per-key metadata
-
-Switching an existing deployment from authoritative to per-key requires a state
-migration. Without it, Terraform will try to destroy the old resource and create
-the new ones, which can fail or cause a brief metadata gap.
-
-```bash
-# 1. Remove the old authoritative resource from state
-terraform state rm 'module.runner.google_compute_project_metadata.runner_metadata'
-
-# 2. Import the individual keys into the new resources
-terraform import 'module.runner.google_compute_project_metadata_item.enable_oslogin[0]' 'projects/<PROJECT_ID>/enable-oslogin'
-terraform import 'module.runner.google_compute_project_metadata_item.runner_id[0]' 'projects/<PROJECT_ID>/gitpod-runner-id'
-
-# 3. Apply — should show no changes
-terraform apply
-```
-
-Replace `<PROJECT_ID>` with your GCP project ID and adjust the module path if
-your module block uses a different name.
-
 ## Releases
 
 New stable releases are published roughly once a week. To get notified when a

variables.tf

@@ -338,7 +338,7 @@ variable "enable_agents" {
 }
 
 variable "use_authoritative_project_metadata" {
-  description = "Use authoritative google_compute_project_metadata (true) or per-key google_compute_project_metadata_item (false). The authoritative resource manages ALL project metadata — keys not listed in this module will be removed. Set to false if other systems or Terraform modules manage project metadata in the same project. Switching from true to false on an existing deployment requires state migration (see README)."
+  description = "When true (default), uses authoritative google_compute_project_metadata which manages all project metadata. Set to false to use per-key metadata items that leave other project metadata untouched."
   type        = bool
   default     = true
 }