Add some application container documentation #2857

Job	Run time
Code (oldstable)	2m 53s
Code (stable)	2m 52s
Client (oldstable, ubuntu-latest)	1m 1s
Code (tip)	2m 53s
Documentation	28s
Client (oldstable, macos-latest)	1m 5s
System (stable, cluster, dir)	2m 52s
Client (oldstable, windows-latest)	2m 12s
System (stable, cluster, btrfs)	2m 52s
Client (stable, ubuntu-latest)	1m 13s
System (stable, cluster, lvm)	2m 52s
Client (stable, macos-latest)	59s
System (stable, cluster, zfs)	2m 51s
Client (stable, windows-latest)	1m 28s
System (stable, cluster, ceph)	2m 49s
System (stable, cluster, random)	2m 52s
System (stable, standalone, dir)	2m 51s
System (stable, standalone, btrfs)	2m 51s
System (stable, standalone, lvm)	2m 52s
System (stable, standalone, zfs)	2m 52s
System (stable, standalone, ceph)	2m 47s
System (stable, standalone, random)	2m 50s
System (oldstable, cluster, dir)	2m 41s
System (oldstable, standalone, dir)	2m 53s
System (tip, cluster, dir)	2m 56s
System (tip, standalone, dir)	2m 53s
	1h 2m 38s

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