tools/: add nixops
This now means we require Nix to be installed globally. This shouldn't
be the case in the long run, but will be until
https://github.com/tweag/rules_nixpkgs/issues/75 gets fixed or we maybe
move from rules_nixpkgs to nix-bundle or something similar.
diff --git a/README b/README
index 641cd51..902b12c 100644
--- a/README
+++ b/README
@@ -3,6 +3,8 @@
This is a monorepo. You'll need bash and Bazel 0.20.0+ to use it.
+You'll also need Nix installed globally in your system until [rules_nixpkgs/75](https://github.com/tweag/rules_nixpkgs/issues/75) is resolved. Or run on NixOS.
+
Getting started
---------------