title: Migrating from npm to yarn when package.json has incorrect versions
body: <p>I recently started working on a pre-existing react-native project, and upon setup I encountered a lot of dependency and versioning errors. The versions on package.json are incorrect for our project, and it caused errors when I ran it until we finally decided to just copy the node_modules folder into my repository from another team member's working repo instead of using <code>npm install</code>.</p>
  
  <p>We'd like to migrate the project to Yarn so that this doesn't continue to happen, but when I try to create a yarn.lock file using either <code>yarn install</code> or <code>yarn install --check-files</code>, I end up with wrong versions and a broken project. Is there any way to generate a yarn.lock file, and potentially a new package.json, based on the versions that are in the node_modules directory?</p>