Add Fira Sans font as per NFDI corporate design

docs/font/FiraSans-Black.ttf

docs/font/FiraSans-BlackItalic.ttf

docs/font/FiraSans-Bold.ttf

docs/font/FiraSans-BoldItalic.ttf

docs/font/FiraSans-ExtraBold.ttf

docs/font/FiraSans-ExtraBoldItalic.ttf

docs/font/FiraSans-ExtraLight.ttf

docs/font/FiraSans-ExtraLightItalic.ttf

docs/font/FiraSans-Italic.ttf

docs/font/FiraSans-Light.ttf

docs/font/FiraSans-LightItalic.ttf

docs/font/FiraSans-Medium.ttf

docs/font/FiraSans-MediumItalic.ttf

docs/font/FiraSans-Regular.ttf

docs/font/FiraSans-SemiBold.ttf

docs/font/FiraSans-SemiBoldItalic.ttf

docs/font/FiraSans-Thin.ttf

docs/font/FiraSans-ThinItalic.ttf

docs/font/OFL.txt