Adding compatibility matrix with Spring Cloud

This won't be needed after this project goes GA since this will be defined in the Spring Cloud BOM
closes gh-78

Author: jonatan-ivanov

README.adoc

@@ -17,6 +17,14 @@ Spring Cloud Sleuth provides Spring Boot auto-configuration for OpenTelemetry ba
 Sleuth configures everything you need to get started.
 This includes where trace data (spans) are reported to, how many traces to keep (sampling), if remote fields (baggage) are sent, and which libraries are traced.
 
+=== Spring Cloud Compatibility
+
+|=======
+| Spring Cloud Sleuth OTel | Spring Cloud
+| 1.0.x | 2020.x
+| 1.1.x | 2021.x
+|=======
+
 === Quick Start
 
 Add Spring Cloud Sleuth to the classpath of a Spring Boot application (together with a Tracer implementation) and you will see trace IDs in logs.