Update guide-en.org

Hi, new guide, I just read through it and although I have been using (not mastering) emacs for the last two years I found it quite insightful and admire your dedicated approach.

Anyway there were a few textual errors I spotted hence the pull request. The diff on line 139 is not really descriptive. I only added a space on that line "some investigation,[ ]I found ".

Keep up the good work!