gnu: Add rust-xdg.

* gnu/packages/crates-io.scm (rust-xdg): New variable.

gnu/packages/crates-io.scm

@@ -1124,3 +1124,23 @@ x86_64-pc-windows-gnu target.  Please don't use this crate directly, depend on
     (license (list license:asl2.0
                    license:expat))))
 
+(define-public rust-xdg
+  (package
+    (name "rust-xdg")
+    (version "2.2.0")
+    (source
+      (origin
+        (method url-fetch)
+        (uri (crate-uri "xdg" version))
+        (file-name (string-append name "-" version ".tar.gz"))
+        (sha256
+         (base32
+          "0mws8a0fr3cqk5nh7aq9lmkmhzghvasqy4mhw6nnza06l4d6i2fh"))))
+    (build-system cargo-build-system)
+    (home-page "https://github.com/whitequark/rust-xdg")
+    (synopsis "Store and retrieve files according to XDG specification")
+    (description
+     "This package provides a library for storing and retrieving files according
+to XDG Base Directory specification")
+    (license (list license:asl2.0
+                   license:expat))))