Consistent instructions and examples

I started off with "hints" that required the poor student to piece
together the information from incomplete bits. A complete example is
like a picture that is worth 1000 words and far clearer.

02_std.zig

@@ -2,13 +2,16 @@
 // Oops! This program is supposed to print a line like our Hello World
 // example. But we forgot how to import the Zig Standard Library.
 //
-// Hint 1: The @import() built-in function returns a value representing
-//         imported code. We need to give that value a name to use it.
-// Hint 2: We use the name "std" in the main function (see below).
-// Hint 3: Imports need to be named by declaring them as "const" values.
-// Hint 4: Take a look at how the previous exercise did this!
+// The @import() function is built into Zig. It returns a value which
+// represents the imported code. It's a good idea to store the import as
+// a constant value with the same name as the import:
 //
-@import("std");
+//     const foo = @import("foo");
+//
+// Please complete the import below:
+//
+
+??? = @import("std");
 
 pub fn main() void {
     std.debug.print("Standard Library.\n", .{});