Add jt graalvm-home

Author: eregon

tool/jt.rb

@@ -731,6 +731,7 @@ def help
       jt sync                                       continuously synchronize changes from the Ruby source files to the GraalVM build
       jt idea                                       generates IntelliJ projects
       jt format                                     run eclipse code formatter
+      jt graalvm-home                               prints the GraalVM home of the RUBY_SELECTOR
 
       you can also put --build or --rebuild in front of any command to build or rebuild first
 
@@ -759,6 +760,10 @@ def launcher
     puts ruby_launcher
   end
 
+  define_method(:'graalvm-home') do
+    puts graalvm_home
+  end
+
   def build(*options)
     project = options.shift
     case project