update README.md with actions badge

README.md

@@ -3,6 +3,8 @@
 A custom Spark data source supporting the [Common Event Format](https://support.citrix.com/article/CTX136146) V25
 standard for logging events.
 
+[![Spark library CI](https://github.com/bp/spark-cef-reader/actions/workflows/main.yml/badge.svg)](https://github.com/bp/spark-cef-reader/actions/workflows/main.yml)
+
 ## Supported Features
 
 * Schema inference. Uses data types for known extensions.
@@ -86,4 +88,4 @@ ISO 8601 formats for where non-standard date formats may have been used.
     MMM dd HH:mm:ss zzz
 
 When reading, if the timezone identifier is omitted, then UTC will be assumed. If the year is omitted then it will
-default to 1970.
+default to 1970.