Support SEO friendly meta tags (#300)

* Support two SEO friendly tags: <meta name="description"> and <meta name="keywords">.

* Support two SEO friendly tags: <meta name="description"> and <meta name="keywords">.

CONTRIBUTORS.md

@@ -64,3 +64,4 @@
 - [Santiago González](https://github.com/netrules)
 - [Codruț Constantin Gușoi](https://www.sdwolfz.pro)
 - [Clément Pannetier](https://clementpannetier.dev)
+- [FantasticMao](https://github.com/FantasticMao)

layouts/_default/baseof.html

@@ -6,8 +6,8 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
 
     {{ with .Site.Params.author }}<meta name="author" content="{{ . }}">{{ end }}
-    {{ with .Site.Params.description }}<meta name="description" content="{{ . }}">{{ end }}
-    {{ with .Site.Params.keywords }}<meta name="keywords" content="{{ . }}">{{ end }}
+    <meta name="description" content="{{ .Description | default (.Summary | default .Site.Params.description ) }}">
+    <meta name="keywords" content="{{ (delimit .Keywords ",") | default .Site.Params.keywords }}">
 
     {{ template "_internal/twitter_cards.html" . }}
     {{ template "_internal/opengraph.html" . }}