a size of a *database* cannot be a sum of the sizes of *all databases*
indicating that a logical size is calculated for a branch
## Describe your changes
## Issue ticket number and link
## Checklist before requesting a review
- [x] i checked the suggested changes
- [x] this is not a core feature
- [x] this is just a docs update, does not require analytics
- [x] this PR does not require a public announcement
Anna Stepanyan
a974602f9f