Fix bug that occurs during the first run

Previously, qfi created the configuration directory, then failed without
running any operations. Not anymore!
Improve detection of which editor to use

The decision of which editor to use is now based on the file's
writability, instead of who owns it. Support for non-existent and
non-accessible files has also been improved. The documentation has been
updated to reflect these changes.
Move links to bottom and fix typo in README.md