docs(user): move wiki/Searx-instances from wiki to docs (WIP)

Move wiki entry https://github.com/asciimoo/searx/wiki/Searx-instances


into user section of the docs (#1785).

links has been ported from markdown to reST by::

      regexpr:        \[([^\]]*)\]\(([^)]*)\)
      substitution:  `\1 <\2>`__

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>