Add note to conda env spec about Conda Apple workaround

$ curl -s https://repo.anaconda.com/pkgs/main/osx-64/repodata.json.bz2 | bunzip2 | grep -A 11 blas-1.0-mkl
    "blas-1.0-mkl.tar.bz2": {
      "build": "mkl",
      "build_number": 1,
      "depends": [],
      "md5": "e2f3248e2a5009a02f7b8e54f83314ef",
      "name": "blas",
      "sha256": "a2c116d511cc8fc0ba53a1e0b4c32ade562c128cc6b6cda4711f13e1a6c4a52c",
      "size": 5620,
      "subdir": "osx-64",
      "timestamp": 1528121955725,
      "version": "1.0"
    },

It looks like it's fixed already: ``` $ curl -s https://repo.anaconda.com/pkgs/main/osx-64/repodata.json.bz2 | bunzip2 | grep -A 11 blas-1.0-mkl "blas-1.0-mkl.tar.bz2": { "build": "mkl", "build_number": 1, "depends": [], "md5": "e2f3248e2a5009a02f7b8e54f83314ef", "name": "blas", "sha256": "a2c116d511cc8fc0ba53a1e0b4c32ade562c128cc6b6cda4711f13e1a6c4a52c", "size": 5620, "subdir": "osx-64", "timestamp": 1528121955725, "version": "1.0" }, ```

Oh, nice. !38