Nomad changes

docs/snippets/ruby/plugins/plugin_extractor.md

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+```ruby title="Ruby"
+require 'kreuzberg'
+
+class CustomPostProcessor
+  def call(result)
+    result['metadata'] ||= {}
+    result['metadata']['processed_by'] = 'CustomPostProcessor'
+    result
+  end
+end
+
+class CustomValidator
+  def call(result)
+    raise StandardError, 'Empty' if result['content'].empty?
+  end
+end
+
+processor = CustomPostProcessor.new
+validator = CustomValidator.new
+
+Kreuzberg.register_post_processor('custom', processor)
+Kreuzberg.register_validator('custom', validator)
+```