Simple .desktop file

[prokoudine]

Here's a simple .desktop file for the app to improve its discoverability in desktop environments. It suggests that there is a brand icon for sviewgl, which is currently missing. Other than that, it should be fine.

Typically, .desktop files get installed to {PREFIX}/applications/, e.g. /usr/share/applications/.

[Andrey Ugolnik]

Thank you. I will add it along with icon file.