[enh] add rss-link which can be detected by browsers

searx/templates/oscar/base.html

     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="generator" content="searx/{{ searx_version }}">
     <meta name="viewport" content="width=device-width, initial-scale=1 , maximum-scale=1.0, user-scalable=1" />
+    {% block meta %}{% endblock %}
     <title>{% block title %}{% endblock %}searx</title>
     
     <link rel="stylesheet" href="{{ url_for('static', filename='css/bootstrap.min.css') }}" type="text/css" />

searx/templates/oscar/results.html

 {% extends "oscar/base.html" %}
 {% block title %}{{ q }} - {% endblock %}
+{% block meta %}<link rel="alternate" type="application/rss+xml" title="Searx search: {{ q }}" href="{{ url_for('index') }}?q={{ q }}&format=rss&{% for category in selected_categories %}category_{{ category }}=1&{% endfor %}pageno={{ pageno+1 }}">{% endblock %}
 {% block content %}
     <div class="row">
         <div class="col-sm-8" id="main_results">