docs(README): Add a note about the ignored resources

Author: pablotp

README.md

@@ -249,7 +249,7 @@ Available targets:
 | <a name="input_enable_streams"></a> [enable\_streams](#input\_enable\_streams) | Enable DynamoDB streams | `bool` | `false` | no |
 | <a name="input_enabled"></a> [enabled](#input\_enabled) | Set to false to prevent the module from creating any resources | `bool` | `null` | no |
 | <a name="input_environment"></a> [environment](#input\_environment) | ID element. Usually used for region e.g. 'uw2', 'us-west-2', OR role 'prod', 'staging', 'dev', 'UAT' | `string` | `null` | no |
-| <a name="input_global_secondary_index_map"></a> [global\_secondary\_index\_map](#input\_global\_secondary\_index\_map) | Additional global secondary indexes in the form of a list of mapped values | <pre>list(object({<br/>    hash_key           = string<br/>    name               = string<br/>    non_key_attributes = list(string)<br/>    projection_type    = string<br/>    range_key          = string<br/>    read_capacity      = number<br/>    write_capacity     = number<br/>  }))</pre> | `[]` | no |
+| <a name="input_global_secondary_index_map"></a> [global\_secondary\_index\_map](#input\_global\_secondary\_index\_map) | Additional global secondary indexes in the form of a list of mapped values. <br/>**Note**: Any changes made to the GSIs will be ignored to avoid drift with auto-scaling ([related issue](https://github.com/hashicorp/terraform-provider-aws/issues/671)). | <pre>list(object({<br/>    hash_key           = string<br/>    name               = string<br/>    non_key_attributes = list(string)<br/>    projection_type    = string<br/>    range_key          = string<br/>    read_capacity      = number<br/>    write_capacity     = number<br/>  }))</pre> | `[]` | no |
 | <a name="input_hash_key"></a> [hash\_key](#input\_hash\_key) | DynamoDB table Hash Key | `string` | n/a | yes |
 | <a name="input_hash_key_type"></a> [hash\_key\_type](#input\_hash\_key\_type) | Hash Key type, which must be a scalar type: `S`, `N`, or `B` for (S)tring, (N)umber or (B)inary data | `string` | `"S"` | no |
 | <a name="input_id_length_limit"></a> [id\_length\_limit](#input\_id\_length\_limit) | Limit `id` to this many characters (minimum 6).<br/>Set to `0` for unlimited length.<br/>Set to `null` for keep the existing setting, which defaults to `0`.<br/>Does not affect `id_full`. | `number` | `null` | no |