Add diagrams for write flow through Raft (#20948)

Add diagrams about write flow through Raft

docs/persistence/README.md

@@ -40,6 +40,7 @@ use [bbolt].
 [boltdb]: https://github.com/boltdb/bolt
 [bbolt]: https://github.com/etcd-io/bbolt
 
+See [diagrams](#diagrams) below for more details on the interaction.
 
 ## State Store
 
@@ -111,3 +112,10 @@ storage.
 
 
 [hashicorp/raft-autopilot]: https://github.com/hashicorp/raft-autopilot
+
+## Diagrams
+### High-level life of a write
+![Overview](./write-overview.png)
+
+### Deep-dive into write through Raft
+![Deep dive](./write-deep-dive.png)