doc: add subscript, pkg-access, and tuple expressions to sample file

doc/sample/Expressions.im

@@ -139,4 +139,22 @@ pkg = { 1, 2, 3, 4, 5 }.
 pkg = { 10, 2 => "Hello", 9, 5 => "World", 14 }.
 pkg = { { 0 }, { 1 }, { y for y in huh } }.
 
-pkg = { x multiplyBy:2 for x in wow if x > 2 }.
+pkg = { x multiplyBy:2 for x in wow if x > 2 }.
+
+pkg->x = 32.
+K = (1 multiplyBy:2, 4).
+
+for (x, y) in pkg do
+	cout put:'{x}: {y}'
+end
+
+pkg[0] = 16.
+
+/* All of these accesses are equivalent */
+pkg['x'] = 32.
+pkg->x = 32.
+pkg put:32 at:'x'.
+
+index = 'x'.
+pkg[index] = 32.
+pkg put:32 at:index.