How to make demo.txt 

Hi Ed,

I appreciate the code you provided . But there is a problem that makes me confused.

According to Step3.5 , Could you please tell me some details about how to make 'demo.txt' and add this codes about how to create to the file [process_mimic.py](https://github.com/mp2893/med2vec/blob/master/process_mimic.py)

Thanks!