Document rfd dependencies in readme

Author: c-git

README.md

@@ -17,6 +17,18 @@ https://woelper.github.io/egui_pick_file/
 
 For native:
 
+On linux install dependencies of [rfd](https://docs.rs/rfd/latest/rfd/index.html) as applicable.
+Copied from https://docs.rs/rfd/latest/rfd/#linux--bsd-backends
+
+> GTK backend is used with the `gtk3` Cargo feature which is enabled by default. The GTK3
+> backend requires the C library and development headers to be installed to build RFD. The package
+> names on various distributions are:
+> | Distribution | Installation Command |
+> | --------------- | ------------ |
+> | Fedora | dnf install gtk3-devel |
+> | Arch | pacman -S gtk3 |
+> | Debian & Ubuntu | apt install libgtk-3-dev |
+
 `cargo run`
 
 For web: