Conflicting README - don't use spaces

[mlsad3]

The README states the following contradiction:

DO NOT USE SPACES OR PUNCTUATION in that string - it can confuse things. Use a string like "timeout" or "button press" or something

Why would you have a string like "button press" if you explicitly warned about spaces?

[mlsad3]

Hi, the code in this heartbeats project looks pretty thorough. Thanks for the great example! I am new to pull requests, but I made one that updates the README to have "button press" as "button_press".