Add clarification to avoid association with event streaming

[Michael Freidgeim]

The name of the library “SQL Stream Store” doesn’t refer to “event sourcing” concept, but someone may associate it with “ Event streaming”.
https://thenewstack.io/event-streaming-and-event-sourcing-the-key-differences/ described the difference.
It will be good in Introduction to clarify the difference to avoid ambiguity.