doc: name of anonymous struct is strange

[bronze1man]

Please document how the name of anonymous struct is get.

const std = @import("std");

pub fn main() !void {
    var stdout_file = try std.io.getStdOut();
    std.debug.warn("{}\n",@typeName(struct{}) );
}

Above code return main()

The document may be come from #160

[andrewrk]

Your example now prints (test.zig:5:38) and I added docs: https://ziglang.org/documentation/master/#struct-naming