Descriptions of experimental features

I noticed https://github.com/apple/foundationdb/pull/11355 adds a page with a list of experimental features and their status, but they each lack descriptions of the features themselves. Maybe I've totally overlooked something, but searching the docs didn't yield any content for some of these features.

Start by reviewing pull request #11355 and the experimental-features page it adds. Identify which listed features lack descriptions, then search the existing FoundationDB documentation for relevant material and determine what each description should cover. Done means the page provides useful descriptions for the applicable experimental features while preserving their status information.

Written by the indexing model from the issue text.