Small changes to the contribution guidelines
Small changes to the contribution guidelines

  * allow PRs against `maintenance` branch for improvements and small
    new features
  * suggest getting in touch on the forum for larger changes

foosel/OctoPrint,Jaesin/OctoPrint,foosel/OctoPrint,foosel/OctoPrint,Jaesin/OctoPrint,foosel/OctoPrint,Jaesin/OctoPrint,Jaesin/OctoPrint