add custom datasets tutorial (#6466)

* add custom datasets tutorial

* python -> bash code blocks

* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* minor review feedback changes

* add working native QA snippet
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

docs/source/_static/js/custom.js

@@ -24,6 +24,7 @@ const versionMapping = {
 // The page that have a notebook and therefore should have the open in colab badge.
 const hasNotebook = [
     "benchmarks",
+    "custom_datasets",
     "multilingual",
     "perplexity",
     "preprocessing",

docs/source/index.rst

@@ -158,6 +158,7 @@ conversion utilities for the following models:
 
     pretrained_models
     examples
+    custom_datasets
     notebooks
     converting_tensorflow_models
     migration