[css-contain-2] (editorial) move sentence for legibility

The last sentence of this paragraph introduces a list, but was separated
from the list by a note which is about the rest of the paragraph.
Reshuffle the text to keep related things closer together.

Author: frivoal

css-contain-2/Overview.bs

@@ -447,9 +447,6 @@ Size Containment</h3>
 	or an <a spec="css-display-3">internal ruby box</a>,
 	or a <a spec="css-display-3" lt="atomic inline">non-atomic</a> <a spec="css-display-3">inline-level</a> box,
 	size containment has no effect.
-	Otherwise, giving an element <dfn export>size containment</dfn>
-	makes its [=principal box=] a <dfn>size containment box</dfn>
-	and has the following effects:
 
 	<wpt>
 	contain-size-001.html
@@ -486,6 +483,10 @@ Size Containment</h3>
 	contain-size-056.html
 	</wpt>
 
+	Otherwise, giving an element <dfn export>size containment</dfn>
+	makes its [=principal box=] a <dfn>size containment box</dfn>
+	and has the following effects:
+
 	1.
 		The [=intrinsic sizes=] of the [=size containment box=]
 		are determined as if the element had no content,