repo: add short section about individual record proof chains #3
Description
In the "Synchronization" section, we could discuss that individual records can be transferred with a "proof" from commit nodes, any intermediate MST nodes, then the record itself, all in a CAR file.
Could also get in to collection-level (or arbitrary sub-tree) synchronization as well. If we do that, should mention the tricks around "covering" the key range by referencing at least one record key "left" and "right" (or be up against the side of entire tree).