Update README

README.adoc

@@ -138,9 +138,9 @@ After you load the extension, a class `Klass` have been generated in the module
 module Xmi
   class EaRoot
     module Mymodule
-      class Klass < Shale::Mapper
-        attribute :base_apply_attribute, Shale::Type::String
-        attribute :tag, Shale::Type::String
+      class Klass < Lutaml::Model::Serializable
+        attribute :base_apply_attribute, :string
+        attribute :tag, :string
 
         xml do
           root "import"
@@ -154,6 +154,15 @@ module Xmi
 end
 ----
 
+=== Limitation
+
+This module is designed to work with XMI files generated by Enterprise
+Architect. It may not work with other XMI files.
+
+Some XML elements, for example `GML:ApplicationSchema`, use `xmlns` as
+attributes. As `Lutaml::Model::Serializable` uses `xmlns` as an internal
+keyword, these attributes will be renamed to `altered_xmlns`.
+
 == Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.