Translate index.md to Turkish (#27093)

* Add index.md for tukish language

* Fix index.md (huggingface/transformers#27088)

* Add 'tr' to additional files

* Update docs/source/tr/_toctree.yml

Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

* Update index.md

---------

Co-authored-by: Mert Yanık <mert.yanik@lcwaikiki.com>
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>

.github/workflows/build_pr_documentation.yml

@@ -14,4 +14,4 @@ jobs:
       commit_sha: ${{ github.event.pull_request.head.sha }}
       pr_number: ${{ github.event.number }}
       package: transformers
-      languages: de en es fr hi it ko pt zh ja te
+      languages: de en es fr hi it ko pt tr zh ja te