chore: add SPDX license

Author: oknozor

src/exec/dbus.rs

@@ -1,3 +1,6 @@
+// Copyright 2022 System76 <[email protected]>
+// SPDX-License-Identifier: GPL-3.0-only
+
 use crate::exec::error::ExecError;
 use crate::exec::graphics::Gpus;
 use crate::DesktopEntry;

src/exec/error.rs

@@ -1,3 +1,6 @@
+// Copyright 2022 System76 <[email protected]>
+// SPDX-License-Identifier: GPL-3.0-only
+
 use std::env::VarError;
 use std::io;
 use std::path::Path;

src/exec/mod.rs

@@ -1,3 +1,6 @@
+// Copyright 2022 System76 <[email protected]>
+// SPDX-License-Identifier: GPL-3.0-only
+
 use crate::exec::error::ExecError;
 use crate::exec::graphics::Gpus;
 use crate::DesktopEntry;