add barebones on-disk mode persistance

Cargo.lock

@@ -111,6 +111,15 @@ dependencies = [
  "libdbus-sys",
 ]
 
+[[package]]
+name = "directories"
+version = "3.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8fed639d60b58d0f53498ab13d26f621fd77569cc6edb031f4cc36a2ad9da0f"
+dependencies = [
+ "dirs-sys",
+]
+
 [[package]]
 name = "dirs"
 version = "1.0.5"
@@ -122,6 +131,17 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "dirs-sys"
+version = "0.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e93d7f5705de3e49895a2b5e0b8855a1c27f080192ae9c32a6432d50741a57a"
+dependencies = [
+ "libc",
+ "redox_users",
+ "winapi",
+]
+
 [[package]]
 name = "evdev-rs"
 version = "0.4.0"
@@ -356,6 +376,7 @@ dependencies = [
 name = "surface-dial-daemon"
 version = "0.1.0"
 dependencies = [
+ "directories",
  "evdev-rs",
  "hidapi",
  "notify-rust",