Before building the project for the first time, make sure that all dependencies are installed with npm install.
Then use npm run package to build the project.
If you are building on a Windows machine, you might see the error "rm -rf... command not found" appear. To fix this, you can use the following command to make npm use Git Bash instead of the Windows command line interpreter:
npm config set script-shell "C:\Program Files\Git\bin\bash.exe"
(The last part may change depending on your Git install location)