gnu: Add rust-json.

* gnu/packages/creates-io.scm (rust-json): New variable.

gnu/packages/crates-io.scm

@@ -293,6 +293,26 @@ primitives to an @code{io::Write}.")
     (license (list license:asl2.0
                    license:expat))))
 
+(define-public rust-json
+  (package
+    (name "rust-json")
+    (version "0.11.14")
+    (source
+      (origin
+        (method url-fetch)
+        (uri (crate-uri "json" version))
+        (file-name (string-append name "-" version ".tar.gz"))
+        (sha256
+         (base32
+          "1hj8c6xj5c2aqqszi8naaflmcdbya1i9byyjrq4iybxjb4q91mq1"))))
+    (build-system cargo-build-system)
+    (home-page "https://github.com/maciejhirsz/json-rust")
+    (synopsis "JSON implementation in Rust")
+    (description "This crate provides a JSON implementation in Rust, reducing
+friction with idiomatic Rust structs to ease interopability.")
+    (license (list license:asl2.0
+                   license:expat))))
+
 (define-public rust-proc-macro2
   (package
     (name "rust-proc-macro2")