[Feature Request] Clarify tolerance percentage format

[Maxim Kupfer]

Is your feature request related to a problem? Please describe.
Clarify that percentage tolerance should be expressed as a decimal value as it could be misinterpreted to be a nominal value and cause silent errors.

Describe the solution you'd like
Simple addition to readme. I actually already have something ready to go here: mbkupfer@e473556, but realized I needed to first open an issue the pull request.

Describe alternatives you've considered
n/a

Additional context
Backstory, I made the mistake of assuming it was nominal and was thinking I was testing a 0.5% tolerance when in fact it was looking at a 50% tolerance! Needless to say, I should have read the source code beforehand, but I'm sure it would be more accessible if we can just add a few extra words in the readme :)

[Claus Herther]

Sounds good to me, thanks