feat(tags): improve usability of tags (#698)

* feat(tags): improve usability of tags

* Tags can be shown also at docs
* Documented tag-related config flags
* Added example tags to the site
* Made rendered tags active

* Move tags listing to ToC

* Hide tags section on no tags

exampleSite/content/docs/getting-started.md

@@ -1,6 +1,9 @@
 ---
 title: Getting Started
 weight: 1
+tags:
+  - Docs
+  - Guide
 next: /docs/guide
 prev: /docs
 ---

exampleSite/content/docs/guide/configuration.md

@@ -1,6 +1,8 @@
 ---
 title: Configuration
 weight: 2
+tags:
+  - Config
 ---
 
 Hugo reads its configuration from `hugo.yaml` in the root of your Hugo site.
@@ -228,6 +230,19 @@ params:
   dateFormat: "January 2, 2006"
 ```
 
+### Tags
+
+To display page tags, set following flags in the config file:
+
+```yaml {filename="hugo.yaml"}
+params:
+  blog:
+    list:
+      displayTags: true
+  toc:
+    displayTags: true
+```
+
 ### Page Width
 
 The width of the page can be customized by the `params.page.width` parameter in the config file: