"Be aware that popular NES games are copyrighted with all rights reserved. In most cases, distributing ROM images of these games infringes copyright. Do not distribute RockNES software along with infringing ROMs."
Beyond that, the wording of a software copyright license depends on exactly what you want to allow, as blargg pointed out. Before you draft the license text, you should decide whether to:
- include or not include source code
- allow or forbid distribution of copies of the emulator from mirror sites
- allow or forbid distribution of copies of the emulator for a fee
- allow or forbid distribution of copies of the emulator bundled with a ROM with consent of the ROM's copyright owner, as is done in Wii Shop Channel