Added Filesystem::has to the readme
Added Filesystem::has to the readme

barryvdh/flysystem,Amrit01/flysystem,sohelrana820/flysystem,hannesvdvreken/flysystem,dshafik/flysystem,concrete5/flysystem,mhlavac/flysystem,mapyo/flysystem,nao-pon/flysystem,twistor/flysystem,dragoonis/Flysystem,sachintaware/flysystem,farmisen/flysystem,rossriley/flysystem,dstockto/flysystem,oswaldderiemaecker/flysystem,CarsonF/flysystem,twistor/flysystem,mhlavac/flysystem