[enh] introduce config/ directory

This commit introduces a config/ directory containing:

* settings.yml (a symlink to searx/settings.yml)
* brand.env (a symlink to utils/brand.env)
* about.md (a new file replacing the previous
  searx/templates/__common__/aboutextend.html)

The intention is that it's easier for admins
to find the files they may want to configure.

Closes #809.

config/about.md

@@ -0,0 +1,4 @@
+<!--
+Below this comment you can write something about your instance if you want to.
+(Whatever you write here is shown at the end of the /about page.)
+-->

config/brand.env

@@ -0,0 +1 @@
+../utils/brand.env

config/settings.yml

@@ -0,0 +1 @@
+../searx/settings.yml

searx/templates/oscar/about.html

@@ -2,5 +2,4 @@
 {% block title %}{{ _('about') }} - {% endblock %}
 {% block content %}
 {{ help.about | safe }}
-{% include "__common__/aboutextend.html" ignore missing %}
 {% endblock %}

searx/templates/simple/about.html

@@ -1,5 +1,4 @@
 {% extends 'simple/base.html' %}
 {% block content %}
 {{ help.about | safe }}
-{% include "__common__/aboutextend.html" ignore missing %}
 {% endblock %}

searx/user_help.py

@@ -44,5 +44,9 @@ def render(app: flask.Flask):
             continue
 
         markdown = pkg_resources.resource_string(__name__, 'help/' + filename).decode()
+
+        if rootname == 'about':
+            markdown += pkg_resources.resource_string(__name__, '../config/about.md').decode()
+
         markdown = define_link_targets + markdown
         HELP[rootname] = mistletoe.markdown(markdown)