Add Github topics to the repository

[mendel5]

It would be great if you could add a few Github topics to this repository. I thought about these:

• https://github.com/topics/sdr
• https://github.com/topics/rtl-sdr
• https://github.com/topics/1090
• https://github.com/topics/1090mhz
• https://github.com/topics/adsb
• https://github.com/topics/ads-b

Thanks!