update the plugin docs with more clarification on the optional config file
update the plugin docs with more clarification on the optional config file

bryancall/trafficserver,rpufky/trafficserver,PSUdaemon/trafficserver,reveller/trafficserver,davidbz/trafficserver,davidbz/trafficserver,duke8253/trafficserver,duke8253/trafficserver,taoyunxing/trafficserver,chenglongwei/trafficserver,chitianhao/trafficserver,PSUdaemon/trafficserver,chitianhao/trafficserver,vmamidi/trafficserver,pbchou/trafficserver,duke8253/trafficserver,chitianhao/trafficserver,pbchou/trafficserver,chenglongwei/trafficserver,rpufky/trafficserver,rpufky/trafficserver,PSUdaemon/trafficserver,vmamidi/trafficserver,chenglongwei/trafficserver,SolidWallOfCode/trafficserver,PSUdaemon/trafficserver,reveller/trafficserver,chenglongwei/trafficserver,chenglongwei/trafficserver,chitianhao/trafficserver,rahmalik/trafficserver,dyrock/trafficserver,dyrock/trafficserver,bryancall/trafficserver,dyrock/trafficserver,persiaAziz/trafficserver,rahmalik/trafficserver,vmamidi/trafficserver,rahmalik/trafficserver,clearswift/trafficserver,pbchou/trafficserver,dyrock/trafficserver,rpufky/trafficserver,davidbz/trafficserver,taoyunxing/trafficserver,reveller/trafficserver,chitianhao/trafficserver,taoyunxing/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,taoyunxing/trafficserver,pbchou/trafficserver,dyrock/trafficserver,clearswift/trafficserver,rpufky/trafficserver,clearswift/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,reveller/trafficserver,chitianhao/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,davidbz/trafficserver,rpufky/trafficserver,davidbz/trafficserver,vmamidi/trafficserver,PSUdaemon/trafficserver,rahmalik/trafficserver,duke8253/trafficserver,persiaAziz/trafficserver,reveller/trafficserver,rpufky/trafficserver,SolidWallOfCode/trafficserver,PSUdaemon/trafficserver,duke8253/trafficserver,persiaAziz/trafficserver,taoyunxing/trafficserver,pbchou/trafficserver,bryancall/trafficserver,taoyunxing/trafficserver,chenglongwei/trafficserver,rahmalik/trafficserver,rahmalik/trafficserver,reveller/trafficserver,rahmalik/trafficserver,rpufky/trafficserver,chenglongwei/trafficserver,duke8253/trafficserver,rpufky/trafficserver,PSUdaemon/trafficserver,clearswift/trafficserver,dyrock/trafficserver,pbchou/trafficserver,persiaAziz/trafficserver,persiaAziz/trafficserver,clearswift/trafficserver,SolidWallOfCode/trafficserver,reveller/trafficserver,dyrock/trafficserver,reveller/trafficserver,taoyunxing/trafficserver,clearswift/trafficserver,reveller/trafficserver,clearswift/trafficserver,persiaAziz/trafficserver,PSUdaemon/trafficserver,bryancall/trafficserver,duke8253/trafficserver,clearswift/trafficserver,clearswift/trafficserver,persiaAziz/trafficserver,taoyunxing/trafficserver,vmamidi/trafficserver,davidbz/trafficserver,rahmalik/trafficserver,taoyunxing/trafficserver,PSUdaemon/trafficserver,rahmalik/trafficserver,persiaAziz/trafficserver,chitianhao/trafficserver,chenglongwei/trafficserver