some license notice

to write somewhere:

```
gfx/2d/indicator-alien* CC By-SA 3.0 by Dozzer (DwarfVader)
gfx/2d/indicator-level* CC By-SA 3.0 by Dozzer (DwarfVader)
gfx/2d/crosshair-* CC By-SA 3.0 by Unvanquished Development (authored by Viech)
gfx/2d/indicator-* CC By-SA 3.0 by Unvanquished Development (authored by Viech)
```