init user documentation

basic configuration with sphinx-quickstart
(cherry picked from commit 1717a0e)
[DOC] define user documentation table of content
Merge remote-tracking branch 'upstream/release-1.10' into features/doc

Conflicts:
	b3/docs/user_documentation/index.rst
moved sphinx setup

Reason:
one setup for the documentation sections (user_guide, developer_reference,....)
I start the sphinx setup in the wrong directory.

Using . to hide build and static folder on unix like systems.
add introduction and change doctree