Add source-pr command

[unional]

Which will automatically:

• create a fork from the source
• Add all typings to the source
• modify package.json to add typings property
• create a PR as follow:

Title: Add typings to the repo

Hi,

I have created <typing repo url> to add TypeScript support for your package.

On the other hand if you accept this PR and release a new patch version on npm, the TypeScript compiler can resolve the typings automatically without any action from the consumer.

Would you be interested in accepting this PR?

Thanks.