Fix syntax error and add clarification in S07-lists

S07-lists.pod

@@ -57,7 +57,8 @@ treated as a single argument to the C<for> loop, thus the name of the rule.
     for (1, 2, 3) { }       # List of 3 things; 3 iterations
     for [1, 2, 3] { }       # Array of 3 things (put in Scalars); 3 iterations
     for @a, @b { }          # List of 2 things; 2 iterations
-    for @a, { }             # List of 1 thing; 1 iteration
+    for (@a,) { }           # List of 1 thing; 1 iteration
+    for @a { }              # List of @a.elems things; @a.elems iterations
 
 The first two are equivalent because parentheses do not actually construct a
 list, but only group. It is the C<< infix:<,> >> operator that forms a list.