[doc] add sphinx-notfound-page

Closes: https://github.com/searxng/searxng/issues/703
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

docs/conf.py

@@ -123,6 +123,7 @@ extensions = [
     'linuxdoc.kfigure',         # Sphinx extension which implements scalable image handling.
     "sphinx_tabs.tabs", # https://github.com/djungelorm/sphinx-tabs
     'myst_parser',  # https://www.sphinx-doc.org/en/master/usage/markdown.html
+    'notfound.extension',  # https://github.com/readthedocs/sphinx-notfound-page
 ]
 
 suppress_warnings = ['myst.domains']
@@ -140,6 +141,10 @@ issues_github_path = "searxng/searxng"
 
 # HTML -----------------------------------------------------------------
 
+# https://searxng.github.io/searxng --> '/searxng/'
+# https://docs.searxng.org --> '/'
+notfound_urls_prefix = '/'
+
 sys.path.append(os.path.abspath('_themes'))
 sys.path.insert(0, os.path.abspath("../utils/"))
 html_theme_path = ['_themes']

requirements-dev.txt

@@ -14,6 +14,7 @@ sphinx-jinja==2.0.1
 sphinx-tabs==3.3.1
 sphinxcontrib-programoutput==0.17
 sphinx-autobuild==2021.3.14
+sphinx-notfound-page==0.8
 myst-parser==0.17.0
 linuxdoc==20211220
 aiounittest==1.4.1