Use CocoaPods:

【1】 Podfile add  pod 'SDWebImage/WebP'

【2】 in Build Settings -- Preprocessor Macros , add SD_WEBP=1

Add files into project:

【1】Cloneand addWebP.framework

  clone the repository usinggit clone --recursive https://github.com/rs/SDWebImage.git

  add full folder of SDWebImage and WebP.framework into your project.  

【2】 in Build Settings -- Preprocessor Macros , add SD_WEBP=1