We haven't added sequences to the documentation yet, sorry! There are two ways:
You can create a region or mesh attachment and check the sequence checkbox. You then specify the start and end frames. Prefix those with zeros if you have zero padding. For example an attachment named boom would use 001 and 030 if your images are named boom001, boom002, ..., boom030. You can then set a key for the sequence to control playback.
The other way is to set an attachment visibility key for each frame in your animation. This is more tedious but gives you a bit more control.
