If you install it from git, you'd have to build and package the code yourself. You shouldn't do this unless you have a good reason to install from git instead of from npm. I'm curious why you want to do this.
But if you're sure you do, then after installing you'll have to run `npm install` then `npm run build` and `npm run package` inside the node_modules/blockly directory. We have a script to do this automatically that you could use. Add `postinstall: blockly-scripts postinstall` to the scripts section of your package.json, and add `@blockly/dev-scripts` to the devDependencies.
Hope that helps!