Update readme to note Return Values mutator
Update readme to note Return Values mutator

oswaldderiemaecker/humbug,mleko/humbug,oswaldderiemaecker/humbug,daniel-mueller/humbug,MakiCode/humbug,padraic/humbug,stof/humbug,JSchwehn/humbug,daniel-mueller/humbug,humbug/humbug,torreytsui/humbug,torreytsui/humbug,humbug/humbug,padraic/humbug,JSchwehn/humbug,eniuz/humbug,mleko/humbug,eniuz/humbug,MakiCode/humbug