[css-align] Add note about justify-self/stretch possibly causing shrinkage.

Author: tabatkins

css-align/Overview.bs

@@ -701,6 +701,9 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 	while still respecting the constraints imposed by 'min-height'/'min-width'/'max-height'/'max-width'.
 	Unless otherwise specified, this value falls back to ''flex-start''.
 
+	Note: The ''justify-self/stretch'' keyword can cause elements to shrink,
+	to fit their container.
+
 	All other values are as defined in [[#alignment-values]], above.
 
 	<hr>