Writer Guide 5.2 Preface ready for review

I have updated and rewritten the Preface to Writer Guide 5.2. Because
I have made extensive additions and changes, I have not tracked
changes from the previous version of the book (4.2).

http://www.odfauthors.org/libreoffice/english/writer-guide/drafts-v5.2/wg5-2-preface/view

I am now working on Chapter 1, Introducing Writer. This chapter also
requires extensive revision. There are so many small changes since
Writer 4.2 that affect information in it.

--Jean