Add global install command to readme
Add global install command to readme

Makes it clearer to install the validator globally, in case you need to run it on other folders (e.g. as part of a testing pipeline for another package)
nellh/bids-validator,Squishymedia/bids-validator,Squishymedia/BIDS-Validator,nellh/bids-validator,nellh/bids-validator