I can't install ruby-debug-ide-0.6.1.gem in the standard location (/usr/bin) because that directory is protected even running sudo:
ERROR: While executing gem ... (Gem::FilePermissionError)
You don't have write permissions for the /usr/bin directory.
So I installed it in /usr/local/bin (with the -n switch)
$ gem list ruby-debug-ide
*** LOCAL GEMS ***
Now how do I get RubyMine to recognize it?