update init template

* add fuzz example
* explain that you might want to delete main.zig or root.zig

lib/init/src/root.zig

@@ -1,3 +1,6 @@
+//! By convention, root.zig is the root source file when making a library. If
+//! you are making an executable, the convention is to delete this file and
+//! start with root.zig instead.
 const std = @import("std");
 const testing = std.testing;