Update documentation around self references (#10)

Signed-off-by: Yoriyasu Yano <[email protected]>

_custom/main.libsonnet

@@ -1 +1,2 @@
-(import './root.libsonnet') + (import './helpers.libsonnet')
+(import './root.libsonnet')
++ (import './helpers.libsonnet')

_custom/root.libsonnet

@@ -37,6 +37,9 @@ local withProvider(name, attrs, alias=null) =
 //
 //   $._ref.null_resource.foo.get('id')
 //
+// NOTE: When chaining and merging multiple calls to withResource, withData, and withModule, you may not be able to use
+// super, self, or $ to get the reference to `_ref`. Instead, make an explicit binding to the outer object using local.
+//
 // Args:
 //   type (string): The resource type to create (e.g., aws_instance, null_resource, etc).
 //   label (string): The label to apply to the instance of the resource.
@@ -77,6 +80,9 @@ local withResource(type, label, attrs) = {
 //
 //   $._ref.data.azurerm_virtual_network.foo.get('id')
 //
+// NOTE: When chaining and merging multiple calls to withResource, withData, and withModule, you may not be able to use
+// super, self, or $ to get the reference to `_ref`. Instead, make an explicit binding to the outer object using local.
+//
 // Args:
 //   type (string): The data source type to create (e.g., aws_instance, local_file, etc).
 //   label (string): The label to apply to the instance of the data source.
@@ -119,6 +125,9 @@ local withData(type, label, attrs) = {
 //
 //   $._ref.module.foo.get('id')
 //
+// NOTE: When chaining and merging multiple calls to withResource, withData, and withModule, you may not be able to use
+// super, self, or $ to get the reference to `_ref`. Instead, make an explicit binding to the outer object using local.
+//
 // Args:
 //   name (string): The name of the module block.
 //   source (string): The source for the module block.