Update task summary (#21067)

* first draft of audio section

* make style

* first draft of computer vision section

* add convnext and encoder tasks

* finish up nlp tasks

* minor edits

* add arch images, more edits

* fix image links

* apply sanchit feedback

* model naming convention

* apply niels vit feedback

* replace detr for segmentation with mask2former

* apply feedback

* apply feedback

docs/source/en/_toctree.yml

@@ -146,6 +146,8 @@
     title: Glossary
   - local: task_summary
     title: What 🤗 Transformers can do
+  - local: tasks_explained
+    title: How 🤗 Transformers solve tasks
   - local: model_summary
     title: Summary of the models
   - local: tokenizer_summary