update documentation

Author: vroldanbet

README.rdoc

@@ -53,9 +53,11 @@ This task will run the test suite and the
   rake rubotest
 
 CI takes too long? If your local box supports
-{Vagrant}[https://www.vagrantup.com/], you can run most of the tests
-in a VM on your local box. For more details and setup instructions, see
-{test/support/vm/openldap/README.md}[https://github.com/ruby-ldap/ruby-net-ldap/tree/master/test/support/vm/openldap/README.md]
+{Docker}[https://www.docker.com/], you can also run integration tests locally.
+Simply run:
+
+  script/ldap-docker
+  INTEGRATION=openldap rake test
 
 == Release