Update gsoc/background.md
Update gsoc/background.md

Co-authored-by: Brigitta Sipőcz <1027e3ac5686021c62353ca55e23b71beaf77cc8@gmail.com>
OpenAstronomy/openastronomy.github.io,OpenAstronomy/openastronomy.github.io,OpenAstronomy/openastronomy.github.io