Document import syntax for compute_project_metadata_item (GoogleCloudPlatform#12746)

Author: chrisst

mmv1/third_party/terraform/website/docs/r/compute_project_metadata_item.html.markdown

@@ -44,12 +44,13 @@ In addition to the arguments listed above, the following computed attributes are
 Project metadata items can be imported using the `key`, e.g.
 
 * `{{key}}`
+* `projects/{{project}}/meta-data/{{key}}`
 
 In Terraform v1.5.0 and later, use an [`import` block](https://developer.hashicorp.com/terraform/language/import) to import project metadata items using one of the formats above. For example:
 
 ```tf
 import {
-  id = "{{key}}"
+  id = "projects/{{project}}/meta-data/{{key}}"
   to = google_compute_project_metadata_item.default
 }
 ```
@@ -58,6 +59,7 @@ When using the [`terraform import` command](https://developer.hashicorp.com/terr
 
 ```
 $ terraform import google_compute_project_metadata_item.default {{key}}
+$ terraform import google_compute_project_metadata_item.default projects/{{project}}/meta-data/{{key}}
 ```
 
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