Update readme.md : simplify composer command
Update readme.md : simplify composer command

Merge the composer.json file modification and the 'composer update' command into one single command
caryl/Laravel-Administrator,stormsson/Laravel-Administrator,jarektkaczyk/Laravel-Administrator,stormsson/Laravel-Administrator,caryl/Laravel-Administrator,hubertnnn/Laravel-Administrator,FrozenNode/Laravel-Administrator,FrozenNode/Laravel-Administrator,inlacer/Laravel-Administrator,caryl/Laravel-Administrator,inlacer/Laravel-Administrator,hubertnnn/Laravel-Administrator,FrozenNode/Laravel-Administrator,inlacer/Laravel-Administrator,caryl/Laravel-Administrator,hubertnnn/Laravel-Administrator,caryl/Laravel-Administrator,stormsson/Laravel-Administrator,hubertnnn/Laravel-Administrator,inlacer/Laravel-Administrator,stormsson/Laravel-Administrator,jarektkaczyk/Laravel-Administrator,jarektkaczyk/Laravel-Administrator,FrozenNode/Laravel-Administrator,jarektkaczyk/Laravel-Administrator