Added info about class coverage map to README

Author: VitalyNikonorov

README.md

@@ -15,10 +15,13 @@ Add
 
 ```ruby
 jacoco.minimum_project_coverage_percentage = 50 # default 0
-jacoco.minimum_package_coverage_map = { # default is empty
+jacoco.minimum_package_coverage_map = { # optional (default is empty)
   'com/package/' => 55,
   'com/package/more/specific/' => 15
 }
+jacoco.minimum_class_coverage_map = { # optional (default is empty)
+  'com/package/more/specific/ClassName' => 15
+}
 jacoco.minimum_class_coverage_percentage = 75 # default 0
 jacoco.files_extension = [".java"] # default [".kt", ".java"]
 jacoco.report("path/to/jacoco.xml", "http://jacoco-html-reports/")