Support for GitHub repositories without a package.json

I'm using yarn to manage some native iOS dependencies by simply adding them:
```sh
yarn add https://github.com/SnapKit/SnapKit#4.2.0
```

But when I try to patch the package:

It would be awesome if the tool could check if a package was downloaded from GitHub. Here's how it looks in `package.json`:

Note: A tag/commit/branch is not required to be specified inside the `package.json` in which case patch-package wouldn't be able to show the patch warning when packages get updated without tapping into the lockfile.