swap codeowner ordering (#7144)

Author: colin-axner

.github/CODEOWNERS

@@ -1,8 +1,13 @@
 # CODEOWNERS: https://help.github.com/articles/about-codeowners/
 
-# Primary repo maintainers
-*       @aaronc @alexanderbez @alessio
+# NOTE: Order is important; the last matching pattern takes the 
+# most precedence.
 
 # Secondary repo maintainers, substitutes of the primary
 # maintainers when they become MIA
 *       @cwgoes @sunnya97
+
+# Primary repo maintainers
+*       @aaronc @alexanderbez @alessio
+
+