Add DataFrame to TOC (#34473)

Author: luisquintanilla

docs/machine-learning/toc.yml

@@ -101,6 +101,8 @@
       href: how-to-guides/load-data-ml-net.md
     - name: Prepare data
       href: how-to-guides/prepare-data-ml-net.md
+    - name: Work with DataFrames
+      href: how-to-guides/getting-started-dataframe.md
     - name: Train, evaluate, and explain the model
       items:
       - name: Train and evaluate a model