sio_record: explain about shutting down
sio_record: explain about shutting down

closes #12

island-org/libsoundio,gityf/libsoundio,andrewrk/libsoundio,davidgranstrom/libsoundio,bestwpw/libsoundio,weizhiwu/libsoundio,andrewrk/libsoundio,WilliamRen/libsoundio,gityf/libsoundio,vanloswang/libsoundio,tmatth/libsoundio,tresf/libsoundio,WilliamRen/libsoundio,davidgranstrom/libsoundio,weizhiwu/libsoundio,tresf/libsoundio,island-org/libsoundio,bestwpw/libsoundio,tmatth/libsoundio,vanloswang/libsoundio