Spanish translation of summarization.mdx (#15947) (#18477)

* Add Spanish translation of summarization.mdx

* Apply suggestions from code review

Co-authored-by: Omar U. Espejel <espejelomar@gmail.com>

Co-authored-by: Omar U. Espejel <espejelomar@gmail.com>

docs/source/es/_toctree.yml

@@ -30,6 +30,8 @@
   - sections:
     - local: tasks/language_modeling
       title: Modelado de lenguaje
+    - local: tasks/summarization
+      title: Generación de resúmenes
     - local: tasks/image_classification
       title: Clasificación de imágenes
     title: Fine-tuning para tareas posteriores
@@ -47,4 +49,4 @@
     title: Filosofía
   - local: bertology
     title: BERTología
-  title: Guías conceptuales
+  title: Guías conceptuales