added contributing.md doc - thanks for the idea, @wuworkshop. and for @sgtphips, @anonregions, @kulbida for contributing
added contributing.md doc - thanks for the idea, @wuworkshop. and for @sgtphips, @anonregions, @kulbida for contributing

NYUMusEdLab/fork-cb,lpatmo/cb,NYUMusEdLab/fork-cb,lpatmo/cb