Tutorial: Mention how to set default editor

Closes coala#94

Author: Adrianzatreanu

Users/Tutorial.rst

@@ -194,6 +194,12 @@ one for the Makefile. This time coala (or better, the
 provide as much helpful information as possible and provides you the
 option to directly open the file in an editor of your choice.
 
+.. note::
+
+    If you want to set a default editor and not be asked for one every time,
+    you can simply add ``editor=$editorName`` (i.e. editor=vim) to your
+    project's ``.coafile`` and it will automatically open in that one.
+
 .. note::
 
     If your editor is already open this may not work, because the other