Better error messages when CLI tools missing

[matthew-andrews]

e.g.

- Please run `npm install --save-dev` or remove `.editorconfig` from this repository or `.gitignore` file.

[rowanmanning]

Alternatively line 82 could also check that the lintspaces command exists?

@if [ -e .editorconfig ] && [ -e package.json ] && [ -x "$(which lintspaces)"  ]; ...