Add help/better description of the encoding preference.

I was expecting, my editor will be opened with the default encoding I mentioned in It'sAllText's options. It looks like it is not the case.

For example, if I have gVim as my editor, gVim always opens with what I mentioned in _vimrc. I would think that beats the purpose of mentioning default encoding in ItsAllText. This option should override what is mentioned in the editor.

This is important since adding some special characters like `»` is not working as a regular user would expect.

**[Edited title by docwhat. Old title: The default encoding mentioned in options is not taken]**