Add documentation on removing local.log

[hotforfeature]

Should add docs to the README to instruct devs on what to do if they want to stop browserstack-local from generating a local.log file. Config needs to include something like this:

module.exports = {
  plugins: {
    browserstack: {
      tunnel: {
        logFile: process.platform === 'win32' ? 'nul' : '/dev/null'
      }
    }
  }
};

[daKmoR]

this solution works nicely :)

thhxxx :)