[enh] add 'kernel-include' reST-directive

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

docs/conf.py

@@ -66,6 +66,7 @@ extensions = [
     "sphinx_issues", # https://github.com/sloria/sphinx-issues/blob/master/README.rst
     "sphinxcontrib.jinja",  # https://github.com/tardyp/sphinx-jinja
     "sphinxcontrib.programoutput",  # https://github.com/NextThought/sphinxcontrib-programoutput
+    'linuxdoc.kernel_include',  # Implementation of the 'kernel-include' reST-directive.
     'linuxdoc.rstFlatTable',    # Implementation of the 'flat-table' reST-directive.
     'linuxdoc.kfigure',         # Sphinx extension which implements scalable image handling.
     "sphinx_tabs.tabs", # https://github.com/djungelorm/sphinx-tabs

docs/dev/reST.rst

@@ -325,8 +325,9 @@ Literal blocks
 
 The simplest form of :duref:`literal-blocks` is a indented block introduced by
 two colons (``::``).  For highlighting use :dudir:`highlight` or :ref:`reST
-code` directive.  To include literals from external files use directive
-:rst:dir:`literalinclude`.
+code` directive.  To include literals from external files use
+:rst:dir:`literalinclude` or :ref:`kernel-include <kernel-include-directive>`
+directive (latter one expands environment variables in the path name).
 
 .. _reST literal: