Update stout documentation after repo merge

[CodingCanuck]

We've merged several smaller stout stub-repos into the main stout repo.

We should similarly merge their documentation. Right now, I think that at least the following stout types lack documentation in the stout repo:

• AtomicBackoff - formerly https://github.com/3rdparty/stout-atomic-backoff
• Notification - formerly https://github.com/3rdparty/stout-notification
• StatefulTally - formerly https://github.com/3rdparty/stout-stateful-tally (though this repo apparently didn't document StatefulTally)
• borrowed_ptr (and related types) - formerly https://github.com/3rdparty/stout-borrowed-ptr

@ArthurBandaryk FYI

[ArthurBandaryk]

We've merged several smaller stout stub-repos into the main stout repo.

We should similarly merge their documentation. Right now, I think that at least the following stout types lack documentation in the stout repo:

• AtomicBackoff - formerly https://github.com/3rdparty/stout-atomic-backoff
• Notification - formerly https://github.com/3rdparty/stout-notification
• StatefulTally - formerly https://github.com/3rdparty/stout-stateful-tally (though this repo apparently didn't document StatefulTally)
• borrowed_ptr (and related types) - formerly https://github.com/3rdparty/stout-borrowed-ptr

@ArthurBandaryk FYI

Agreed Alex! Will do later!