german docs translation (#18544)

* Create _config.py

* Create _toctree.yml

* Create index.mdx

not sure about "du / ihr" oder "sie"

* Create quicktour.mdx

* Update _toctree.yml

* Update build_documentation.yml

* Update build_pr_documentation.yml

* fix build

* Update index.mdx

* Update quicktour.mdx

* Create installation.mdx

* Update _toctree.yml

docs/source/de/_toctree.yml

@@ -0,0 +1,8 @@
+- sections:
+  - local: index
+    title: 🤗 Transformers
+  - local: quicktour
+    title: Schnellstart
+  - local: installation
+    title: Installation
+  title: Erste Schritte