There are a number of small issues with the default-provided main.d file that have been bugging me for a while:

 * The module with `main` contains an explicit module statement, for which I can think of no justification

 * The main function uses an `int` return type without actually needing it, resulting in the boilerplate `return 0;` statement

 * The main function receives the program argument list but doesn't use it. Even if it did use it, it's named `argv` even though there is no `argc` in D; `argv` is still potentially a decent name, but I think `args` is more common, and has no implication of `argc`

I suggest changing it to one of either:
-----
void main()
{
    import std.stdio : writeln;
    writeln("hello, world");
}
-----
Or
-----
import std.stdio;

void main()
{
    writeln("hello, world");
}
-----

The former is probably the most conducive to remaining correct after tweaking.
The latter is probably the most consistently used hello-world example for D2 (e.g. it's used on the front page of wiki.dlang.org).