[css-align] Add two issues about the legacy keyword.

Author: tabatkins

css-align/Overview.bs

@@ -984,6 +984,19 @@ Inline/Main-Axis Alignment: the 'justify-items' property</h3>
 
 	Other values have no special handling and are merely passed to 'justify-self'.
 
+	Issue: The ''justify-items/auto'' keyword exists solely to implement the ''legacy'' inheritance property.
+	We could just rename it to ''legacy'',
+	since it computes away to ''justify-items/normal'' unless you're using ''legacy'' anyway.
+
+	Issue: The ''legacy'' keyword acts weird,
+	to make it behave like an inherited value
+	even though this property is not inherited.
+	We don't mix inheritance and non-inheritance anywhere else,
+	because it's a bad code smell.
+	Should we remove ''legacy'' and make a separate inheriting property for it?
+	Or just drop the behavior entirely and let it remain special HTML magic?
+
+
 <h3 id='align-items-property'>
 Block/Cross-Axis Alignment: the 'align-items' property</h3>