Update README.md file
Update README.md file

Corrected instructions about the location of the snipcart.yaml file. It goes in user/plugins/snipcart/, not user/config/. Or at any rate that's where it is in the shop skeleton, and putting it in the user/config/ folder does nothing.
couellet/grav-plugin-snipcart,getgrav/grav-plugin-snipcart,getgrav/grav-plugin-snipcart,couellet/grav-plugin-snipcart,getgrav/grav-plugin-snipcart,couellet/grav-plugin-snipcart