Add missing reference docs for JMH directives

Author: Gedochao

modules/directives/src/main/scala/scala/build/preprocessing/directives/Benchmarking.scala

@@ -16,6 +16,8 @@ import scala.build.{Positioned, options}
 import scala.cli.commands.SpecificationLevel
 
 @DirectiveGroupName("Benchmarking options")
+@DirectiveExamples(s"//> using jmh")
+@DirectiveExamples(s"//> using jmh true")
 @DirectiveExamples(s"//> using jmhVersion ${Constants.jmhVersion}")
 @DirectiveUsage(
   "//> using jmh _value_ | using jmhVersion _value_",

website/docs/reference/directives.md

@@ -14,6 +14,10 @@ Add benchmarking options
 `//> using jmhVersion` _value_
 
 #### Examples
+`//> using jmh`
+
+`//> using jmh true`
+
 `//> using jmhVersion 1.37`
 
 ### BuildInfo