Install github's "Stale bot" in the repository

[QuantumNovice]

https://github.com/marketplace/stale

[cclauss]

I am usually not a fan of stalebot but for this repo currently with 150+ open PRs, it might not be a bad idea.

I would also be interested to see TheAlgorithms sign up for the GitHub Actions beta. Doing so would enable us to replace our Travis setup. https://github.blog/2019-08-08-github-actions-now-supports-ci-cd/

[github-actions]

Stale issue message

[cclauss]

No one has admin rights to this repo.