Improve error message when grammar is Null

[n-riesco]

Hi,

In regard to @n-riesco 's comment "please could you also confirm that the file %APPDATA%\jupyter\kernels\javascript\kernel.json":
I don't seem to have the folder kernels. (I guess that explains why Atom says it can't find the kernels?)

regarding the instructions on https://nteract.io/kernels , I don't quit understand where to run these commands?

I have Hydrogen Installed in Atom
I have Jupyter and IPython Installed (via Anaconda, that should be enough, right? )
When trying to run "hydrogen:update-kernels" in Atom, I get "no matches found"

Originally posted by @m-y-reich in #1261 (comment)