[doc] describe 'make books/{name}.html' and 'books/{name}.pdf'

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

docs/dev/makefile.rst

@@ -150,6 +150,35 @@ Documentation <contrib docs>` section.  If you want to edit the documentation
 read our :ref:`make docs-live` section.  If you are working in your own brand,
 adjust your :ref:`Makefile setup <makefile setup>`.
 
+.. _make books:
+
+``make books/{name}.html books/{name}.pdf``
+===========================================
+
+.. _intersphinx: https://www.sphinx-doc.org/en/stable/ext/intersphinx.html
+.. _XeTeX: https://tug.org/xetex/
+
+.. sidebar:: info
+
+   To build PDF a XeTeX_ is needed, see :ref:`buildhosts`.
+
+
+The ``books/{name}.*`` targets are building *books*.  A *book* is a
+sub-directory containing a ``conf.py`` file.  One example is the user handbook
+which can deployed separately (:origin:`docs/user/conf.py`).  Such ``conf.py``
+do inherit from :origin:`docs/conf.py` and overwrite values to fit *book's*
+needs.
+
+With the help of Intersphinx_ (:ref:`reST smart ref`) the links to searx’s
+documentation outside of the book will be bound by the object inventory of
+``DOCS_URL``.  Take into account that URLs will be picked from the inventary at
+documentation's build time.
+
+Use ``make docs-help`` to see which books available:
+
+.. program-output:: bash -c "cd ..; make --no-print-directory docs-help"
+   :ellipsis: 0,-6
+
 
 .. _make gh-pages:
 

docs/dev/reST.rst

@@ -319,6 +319,9 @@ To list all anchors of the inventory (e.g. ``python``) use:
 .. code:: sh
 
    $ python -m sphinx.ext.intersphinx https://docs.python.org/3/objects.inv
+   ...
+   $ python -m sphinx.ext.intersphinx https://searx.github.io/searx/objects.inv
+   ...
 
 Literal blocks
 ==============

docs/user/conf.py

@@ -4,6 +4,8 @@
 project   = 'Searx User-HB'
 version   = release = VERSION_STRING
 
+intersphinx_mapping['searx'] = (DOCS_URL, None)
+
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).

docs/user/own-instance.rst

@@ -56,9 +56,9 @@ results.
 I see. What about private instances?
 ------------------------------------
 
-If users run their own instances, everything is in their control: the source
-code, logging settings and private data.  Unknown instance administrators do not
-have to be trusted.
+If users run their :ref:`own instances <installation>`, everything is in their
+control: the source code, logging settings and private data.  Unknown instance
+administrators do not have to be trusted.
 
 Furthermore, as the default settings of their instance is editable, there is no
 need to use cookies to tailor searx to their needs.  So preferences will not be