Simplify language/description to add new Sphinx project

Shorten and split some sentences. Add link to manual converter.
Mark OpenOffice manual as legacy

Give advice to stop using SWX, since this format is marked as outdated in the introduction already.
[TASK] Fix wrong file extension

Correct the extension name for OO files ("SXW" and not "SWX").
Merge pull request #8 from pixelbrackets/patch-1

Simplify language/description to add new Sphinx project