title: Assign a number to participants in tkinter
body: <p>I've searched all day for some code to help me figured out how to approach my problem but I did not managed to get something, so I hope once again in your help.
  I'd like to add to the people that complete my form a number that increase of one for every person. I really don't know where to start from: first I may need a function to read the last number saved to increas by one in the excel file so that is not reapeated right? Then I don't know if is better to create a button to do so or already show the number in a label. Also I should be able to choose the number where to start, since I'd make my program start in various computer and the renge of number use should be different.
  Can somebody help me figure out how to solve this?
  Thank you</p>