how to add git repo in my package.json

You can just open the package.json file with any editor and add the following in the main object

"repository": {
    "type": "git",
    "url": "https://github.com/sonyzach/usfm-validator.git"
},

also I think you should add the .git version

Just run below command:

npm install --save https://github.com/sonyzach/usfm-validator

or

yarn add https://github.com/sonyzach/usfm-validator