[css-multicol] Fix link to formatting contexts. Fix grammar in note.

Author: fantasai

css-multicol/Overview.bs

@@ -952,10 +952,10 @@ Spanning columns</h2>
 			Content in the normal flow that appears before the
 			element is automatically balanced across all columns before the
 			element appears.
-			The element <a>becomes a formatting context</a>.
+			The element establishes a new <a>formatting context</a>.
 
-			Note: The element establishing a formatting content does not
-			depend of whether the element is a descendent of a multicol or not.
+			Note: Whether the element establishes a new <a>formatting context</a>
+			does not depend on whether the element is a descendent of a multicol or not.
 			When 'column-span' is ''column-span/all'', it always does.
 			This helps with robustness of designs to later revisions
 			that remove the multicol,