[mod] searxng_extras - minor improvements

- fix docs/searxng_extra/standalone_searx.py.rst
- add SPDX tag
- pylint standalone_searx.py and update_wikidata_units.py

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

searxng_extra/update/update_external_bangs.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python
 # lint: pylint
+# SPDX-License-Identifier: AGPL-3.0-or-later
 """
 Update searx/data/external_bangs.json using the duckduckgo bangs.