Add keywords in HTML header for Orekit pages

_config.yml

@@ -6,6 +6,8 @@ description: >  # This means to ignore newlines until "baseurl:"
   Orekit is a free library providing accurate and efficient low level
   components for the development of flight dynamics applications.
 
+keywords: orekit, space, space mechanics, space flight, orbit determination, orbit propagation, java, library, open source
+
 # The subpath of your site, e.g. /blog/
 baseurl: ""
 # The base hostname & protocol for your site without a trailing slash.

_includes/head_orekit.html

@@ -7,6 +7,7 @@
 
     <title>{% if page.title %}{{ page.title }}{% else %}{{ site.title }}{% endif %}</title>
     <meta name="description" content="{% if page.excerpt %}{{ page.excerpt | strip_html | strip_newlines | truncate: 160 }}{% else %}{{ site.description | strip_newlines }}{% endif %}"/>
+    <meta name="keywords" content="{% if page.keywords %}{{ page.keywords }}{% else %}{{ site.keywords }}{% endif %}"/>
 
     <link rel="stylesheet" href="{{ "/css/bootstrap.min.css" | prepend: site.baseurl }}"/>
     <link rel="stylesheet" href="{{ "/css/syntax.css" | prepend: site.baseurl }}"/>