Create .desktop file

[jack-ullery]

Is your feature request related to a problem? Please describe.
This was recently mentioned to me by @54m43lJ, but it would probably be a good time to create a .desktop file for our application. A desktop entry would allow users to start AppAnvil from their application menu, instead of just the command-line.

A while ago, I experimented with creating a .desktop file for AppAnvil, but didn't spend enough time to refine it for the repository. I can't seem to find this work, and starting from scratch wouldn't be very difficult.

Describe the solution you'd like
We would need to create a .desktop file (put it in ./resources) and have it automatically configured/installed by CMake.

We could also use the configure_file() function of CMake to automatically configure this file to point to AppAnvil's install location, which could be different depending on CMAKE_INSTALL_PREFIX.

We could also use the install() function of CMake to copy the file over to the correct directory. However, different distributions might handle installing desktop files differently. We could also look into using something like the desktop-file-install command.

[Skeevert]

Greetings, I would like to deal with this issue. I'll send a pull request in a day.

[jack-ullery]

Thanks again