enable stale bot

[piramiday]

propose to close issues after 6 months of inactivity, finally close after another month.

https://github.com/apps/stale
https://github.com/probot/stale

[piramiday]

thanks for merging this! 👍
I believe this will help immensely in keeping the number of issues down to a manageable level.
(it goes without saying that you should tweak the parameters to what you think is best.)

final comment: you have to explicitly install the stale bot in the repo:

Usage

1. Configure the GitHub App
2. Create .github/stale.yml based on the following template.
3. It will start scanning for stale issues and/or pull requests within an hour.

[piramiday]

thanks for installing the bot!

lots of issues will be closed unless the people involved commented to keep those open.
in another month, when the stale bot will actually start closing issues, you should have a leaner repository so you can focus on working on the problems that are still-relevant (if you have time, that is).