Improve search engine result presentation

- best to keep title length under 55 characters
- descrioption should not be longer than 150-160 characters

layouts/header.html

@@ -4,7 +4,7 @@
     <meta charset="utf-8">
     <meta http-equiv="X-UA-Compatible" content="IE=edge">
     <meta name="viewport" content="width=device-width, initial-scale=1">
-    <meta name="description" content="Prometheus monitoring system and time series database">
+    <meta name="description" content="An open-source monitoring system with a dimensional data model, flexible query language, efficent time series database and modern alerting approach.">
     <meta name="keywords" content="prometheus, monitoring, monitoring system, time series, time series database, alerting, metrics, telemetry">
     <meta name="author" content="Prometheus">
 
@@ -32,7 +32,7 @@
     <% if @item[:title] %>
     <title><%= @item[:title] %> | Prometheus</title>
     <% else %>
-    <title>Prometheus - Service monitoring and time series database</title>
+    <title>Prometheus - Monitoring system &amp; time series database</title>
     <% end %>
 
     <!-- Bootstrap core CSS -->