include a sequence diagram into readme

Author: Ivan Rylach

README.md

@@ -1,5 +1,11 @@
 # Idempotent Requests
+Idempotent Requests Server provides API to allocate and record a captured request.
 
-![CI workflow](https://github.com/checkr/idempotent-requests/actions/workflows/ci.yml/badge.svg)
+## Project status
 
-![Release workflow](https://github.com/checkr/idempotent-requests/actions/workflows/release.yml/badge.svg)
+ ![CI workflow](https://github.com/checkr/idempotent-requests/actions/workflows/ci.yml/badge.svg)
+ ![Release workflow](https://github.com/checkr/idempotent-requests/actions/workflows/release.yml/badge.svg)
+
+## Example request sequence
+
+![sequence](./docs/sequence.png)