Add meta for elixir & rebar.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>

pkgs/development/tools/build-managers/rebar/default.nix

@@ -15,4 +15,21 @@ stdenv.mkDerivation {
     mkdir -p $out/bin
     cp rebar $out/bin/rebar
   '';
+
+  meta = {
+    homepage = "https://github.com/rebar/rebar";
+    description = "Erlang build tool that makes it easy to compile and test Erlang applications, port drivers and releases.";
+
+    longDescription = ''
+      rebar is a self-contained Erlang script, so it's easy to
+      distribute or even embed directly in a project. Where possible,
+      rebar uses standard Erlang/OTP conventions for project
+      structures, thus minimizing the amount of build configuration
+      work. rebar also provides dependency management, enabling
+      application writers to easily re-use common libraries from a
+      variety of locations (git, hg, etc).
+      '';
+
+    platforms = stdenv.lib.platforms.linux;
+  };
 }