Update documentation of @panic
Update documentation of @panic

The default panic handler implementation was moved to `builtin.zig`.

andrewrk/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,raulgrell/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig