Fixed reference to non-existing image in README
Fixed reference to non-existing image in README

mplewis/platformio,TimJay/platformio,mseroczynski/platformio,aphelps/platformio,platformio/platformio,awong1900/platformio,aphelps/platformio,bkudria/platformio,eiginn/platformio,awong1900/platformio,bkudria/platformio,dkuku/platformio,TimJay/platformio,platformio/platformio-core,atyenoria/platformio,bkudria/platformio,aphelps/platformio,TimJay/platformio,mcanthony/platformio,aphelps/platformio,jrobeson/platformio,jrobeson/platformio,bkudria/platformio,jrobeson/platformio,awong1900/platformio,ZachMassia/platformio,jrobeson/platformio,platformio/platformio-core,TimJay/platformio,TimJay/platformio,valeros/platformio