docs: 📝 add learning objectives section to lesson template (#95)

## Description

To help align the structure of this section across sessions. 

## Reviewer Focus

This PR needs a quick review. 

## Checklist

- [X] Ran spell-check
- [X] Formatted Markdown

sessions/lesson.qmd

@@ -4,7 +4,15 @@
 
 <!-- TODO: Add an introduction here -->
 
-**Session objectives**:
+## Learning objectives
+
+The **overall learning** outcome of this session is to:
+
+1.  
+
+Specific **objectives** are to:
+
+1.  
 
 ## TODO: Section