README.md: Update description to match version v0.3-DL-2

Author: IepIweidieng

README.md

@@ -1,8 +1,8 @@
 # bbs-ruby
 
-An environment for running Ruby code on MapleBBS/PttBBS with `$SAFE` level protection.
+An environment for running Ruby code on MapleBBS/PttBBS with security mechanisms implemented with library whitelist on mruby or `$SAFE` level on CRuby.
 
-Ruby 1.9 - 2.2 are supported; using Ruby 2.2 is recommended.
+Both mruby and CRuby 1.9 - 2.2 are supported; using mruby is recommended.
 
 License: MIT\
 Original Author: Zero Cho