How-to on iproto replication

**Doc page:** TBD. Somewhere around https://www.tarantool.io/en/doc/latest/reference/internals/iproto/replication/
**SME:** @ bitgorbovsky @ KAPANDR 

# Details

Add a step-by-step instruction on setting up iproto interaction for replication:
1. IPROTO_JOIN or IPROTO_FETCH_SNAPSHOT
2. IPROTO_SUBSCRIBE

Possibly, more details or an example is also needed.