docs: fix missing required attribute in example (#80)

Author: ethanndickson

docs/resources/template.md

@@ -47,6 +47,7 @@ resource "coderd_template" "ubuntu-main" {
       id   = coderd_user.coder1.id
       role = "admin"
     }]
+    groups = []
   }
 }
 ```

examples/resources/coderd_template/resource.tf

@@ -32,5 +32,6 @@ resource "coderd_template" "ubuntu-main" {
       id   = coderd_user.coder1.id
       role = "admin"
     }]
+    groups = []
   }
 }