Minimal YAML frontmatter (#387)

* Minimal YAML frontmatter

* Modification via prefix.md, not direct

README.md

@@ -1,3 +1,10 @@
+---
+page_type: sample
+languages:
+- python
+products:
+- azure-machine-learning
+---
 # Azure Machine Learning Examples
 
 [![smoke](https://github.com/Azure/azureml-examples/workflows/smoke/badge.svg)](https://github.com/Azure/azureml-examples/actions?query=workflow%3Asmoke)

prefix.md

@@ -1,3 +1,10 @@
+---
+page_type: sample
+languages:
+- python
+products:
+- azure-machine-learning
+---
 # Azure Machine Learning Examples
 
 [![smoke](https://github.com/Azure/azureml-examples/workflows/smoke/badge.svg)](https://github.com/Azure/azureml-examples/actions?query=workflow%3Asmoke)