Clarify missing css file error message

[RolfBabijn]

As a new user I came across a very confusing error message which took me way too long to debug. I was trying to set up the new webpack-encore configuration to use the twig-loader. I followed all the instructions, but I kept getting the following error:

./node_modules/twig/twig.js contains a reference to the file path.
This file can not be found, please check it for typos or update it if the file got moved.

Since "file path" is a very commonly used phrase, I did not realise that it meant that the file (or dependency) path was missing. Searching online also didn't help me out.

I'm not sure what the best solution is (or if it's an accepted edge case), but having it highlighted could save some new users a lot of time and frustration when starting out. I decided on simple quotes since that works regardless of colours are enabled in the terminal.

[RolfBabijn]

@stof: Thanks for the review. I've updated the code accordingly. Could you check the changes? I've left the discussion open for you to comment on or to resolve/close.

[weaverryan]

Wow, this is wonderful! Even I had to stare for a minute at the error message you received and check the code... I was also confused! Thank you so much for, at the very least, saving others the pain in the future. Cheers Rolf!