units: add readline dependency

The dependency on `readline` is for tab-completion support. This commit
also enables tests and adds meta information.

pkgs/tools/misc/units/default.nix

···
-{stdenv, fetchurl}:
+{ stdenv, fetchurl, readline }:
+
 stdenv.mkDerivation rec {
   name = "units-${version}";
   version = "2.12";
···
     sha256 = "1jxvjknz2jhq773jrwx9gc1df3gfy73yqmkjkygqxzpi318yls3q";
   };
 
-  meta = {
+  buildInputs = [ readline ];
+
+  doCheck = true;
+
+  meta = with stdenv.lib; {
     description = "Unit conversion tool";
-    platforms = stdenv.lib.platforms.linux;
+    homepage = https://www.gnu.org/software/units/;
+    license = [ licenses.gpl3Plus ];
+    platforms = stdenv.lib.platforms.all;
   };
 }