REVIEW: 114966

Updating documentation to reflect recent change in program start-up:
KBibTeX shows the "Default Bibliography Editor" window after the first
run to ask the user to set KBibTeX as the default handler for various
bibliography filenames.
This patch updates the documentation to explain this change. It also
explains how to revert the changed handler settings.
Patch by Yuri Chornoivan <yurchor@ukr.net>