[css-grid] Clarify that only content-based tracks are stretched by justify-content per <https://lists.w3.org/Archives/Public/www-style/2015Jan/0183.html>

Author: fantasai

css-grid/Overview.bs

@@ -1033,6 +1033,10 @@ Repeating Rows and Columns: the ''repeat()'' notation</h4>
 	Note: It is expected that a future level of this specification will define a value to be inserted between the repetitions,
 	similar to the argument of the <code>Array#join</code> method in JavaScript.
 
+	Issue: There's no ability currently to fill the grid with columns based on number of items.
+	See <a href='https://lists.w3.org/Archives/Public/www-style/2015Feb/0203.html'>thread</a>.
+	(This might be better handled in Flexbox.)
+
 <h4 id='fr-unit'>
 Flexible Lengths: the ''fr'' unit</h4>
 
@@ -2652,6 +2656,8 @@ Grid Sizing Algorithm</h3>
 			and the tracks are aligned within the <a>grid container</a>
 			according to the 'align-content' and 'justify-content' properties.
 			<span class="note">Note: This can introduce extra space within or between tracks.</a>
+			(When introducing space within tracks,
+			only tracks with an <a lt="intrinsic sizing function">intrinsic</a> <a>max track sizing function</a> accept space.)
 	</ol>
 
 	Once the size of each <a>grid area</a> is thus established,