🌐 [i18n-KO] Translated roberta.md to Korean (#37069)

* docs: ko: roberta.md

* fix: manual edits

* Apply suggestions from code review

Co-authored-by: Woojun Jung <46880056+jungnerd@users.noreply.github.com>
Co-authored-by: YONGSANG <71686691+4N3MONE@users.noreply.github.com>

---------

Co-authored-by: Woojun Jung <46880056+jungnerd@users.noreply.github.com>
Co-authored-by: YONGSANG <71686691+4N3MONE@users.noreply.github.com>

docs/source/ko/_toctree.yml

@@ -480,8 +480,8 @@
         title: (번역중) RemBERT
       - local: in_translation
         title: (번역중) RetriBERT
-      - local: in_translation
-        title: (번역중) RoBERTa
+      - local: model_doc/roberta
+        title: RoBERTa
       - local: in_translation
         title: (번역중) RoBERTa-PreLayerNorm
       - local: in_translation