Fix setup.rst diagnostic command in documentation

[solonovamax]

• Fix for not including the rtorrent process when invoked via rtorrent, rather than /usr/bin/rtorrent.
• Don't include any text editors editing .rtorrent.rc (For example: nano ~/.rtorrent.rc

[brianredbeard]

out of curiosity, based on the stated outcome why not use pgrep (https://www.man7.org/linux/man-pages/man1/pgrep.1.html)?

[solonovamax]

out of curiosity, based on the stated outcome why not use pgrep ( https://www.man7.org/linux/man-pages/man1/pgrep.1.html )?

1. Because I wanted to modify the already existing command
2. Because I didn't remember about pgrep and I now want to pretend that was 100% intentional