chore(docs): update documentation for coder_workspace_tags (#15620)

Adds documentation relating to
https://github.com/coder/coder/issues/15087 and
https://github.com/coder/coder/issues/15427

See also: https://github.com/coder/coder/pull/15578

examples/workspace-tags/README.md

@@ -15,6 +15,14 @@ Template administrators can use static tags to control workspace provisioning, l
 
 By using `coder_workspace_tags` and `coder_parameter`s, template administrators can allow dynamic tag selection, avoiding the need to push the same template multiple times with different tags.
 
+# Notes
+
+- You will need to have an [external provisioner](https://coder.com/docs/admin/provisioners#external-provisioners) with the correct tagset running in order to import this template.
+- When specifying values for the `coder_workspace_tags` data source, you are restricted to using a subset of Terraform's capabilities.
+- You must specify default values for all data sources and variables referenced by the `coder_workspace_tags` data source.
+
+See [Workspace Tags](https://coder.com/docs/templates/workspace-tags) for more information.
+
 ## Development
 
 Update the template and push it using the following command:

examples/workspace-tags/main.tf

@@ -54,8 +54,8 @@ data "coder_parameter" "project_name" {
   name         = "project_name"
   display_name = "Project name"
   description  = "Specify the project name."
-
-  mutable = false
+  default      = "SUPERSECRET"
+  mutable      = false
 }
 
 data "coder_parameter" "feature_cache_enabled" {