Add text indicating that "snapshots" are tab backups

[Kelvets]

Description

I'm migrating from Simple Tab Groups to this, and I pressed Ctrl + F to search in the Options list for "backup" to find out how I could back up my tab groups with this extension and recover all my tabs in case Firefox crashed and lost data. It found no result. Turns out this feature is called "snapshots", which is absolutely not obvious what it does for people who are not from a programming background.

I would suggest that the "Snapshots" menu category gets renamed to "Snapshots (tab backups)" so that people not used to the terminology can also easily find this feature.