use xdg convention for log file location putting it in .cache (see #27)

Author: Stephan Dilly

README.md

@@ -63,11 +63,16 @@ cargo install gitui
 
 # diagnostics:
 
-to enable logging to `~/.gitui/gitui.log`:
+to enable logging:
 ```
 GITUI_LOGGING=true gitui
 ```
 
+this will log to:
+* `$HOME/Library/Caches/gitui/gitui.log` (mac)
+* `$XDG_CACHE_HOME/gitui/gitui.log` (linux using `XDG`) 
+* `$HOME/.cache/gitui/gitui.log` (linux)
+
 # inspiration
 
 * https://github.com/jesseduffield/lazygit

src/main.rs

@@ -152,8 +152,8 @@ fn start_terminal<W: Write>(
 
 fn setup_logging() {
     if env::var("GITUI_LOGGING").is_ok() {
-        let mut path = dirs::home_dir().unwrap();
-        path.push(".gitui");
+        let mut path = dirs::cache_dir().unwrap();
+        path.push("gitui");
         path.push("gitui.log");
         fs::create_dir(path.parent().unwrap()).unwrap_or_default();