Document how to configure the check task to verify aggregated coverage (thanks @Quizzie)

Author: maiflai

README.md

@@ -76,6 +76,14 @@ This will produce a report into `build/scoverage-aggregate` directory.
 
 Aggregation uses same flags as reporting for enabling/disabling different output types.
 
+For checking coverage of the aggregated result, configure the checkScoverage task:
+
+```groovy
+checkScoverage {
+     reportDir = file("$buildDir/scoverage-aggregate")
+}
+```
+
 CheckScoverage
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