Moved exercises to exercises because exercises

exercises/02_std.zig

@@ -0,0 +1,24 @@
+//
+// Oops! This program is supposed to print a line like our Hello World
+// example. But we forgot how to import the Zig Standard Library.
+//
+// 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:
+//
+//     const foo = @import("foo");
+//
+// Please complete the import below:
+//
+
+??? = @import("std");
+
+pub fn main() void {
+    std.debug.print("Standard Library.\n", .{});
+}
+
+// Going deeper: imports must be declared as "constants" (with the 'const'
+// keyword rather than "variables" (with the 'var' keyword) is that they
+// can only be used at "compile time" rather than "run time". Zig evaluates
+// const values at compile time. Don't worry if none of this makes sense
+// yet! See also this answer: https://stackoverflow.com/a/62567550/695615