Update outdated plugin documentation

Author: jamos-tay

docs/userGuide/plugins/filterTags.mbdf

@@ -15,20 +15,27 @@ Tags are specified by the `tags` attribute, **and can be attached to any HTML el
 <p tags="language--python">print("Hello world")</p>
 ```
 
-You need to specify the tags to include in `site.json`, under the `tags` option:
+You need to specify the tags to include in the `pluginsContext`, under `tags`:
 
 ```json
 {
   ...
-  "tags": ["language--java"]
+  "plugins" : [
+    "filterTags"
+  ],
+  "pluginsContext" : {
+    "filterTags" : {
+      "tags": ["language--java"]
+    }
+  }
 }
 ```
 
 All other tagged elements will be filtered out. In this case, only the element with the `language--java` tag will be rendered. This is helpful when creating multiple versions of a page without having to maintain separate copies.
 
 </div>
 
-If the `tags` option is not specified in `site.json`, all tagged elements will be rendered.
+If the `filterTags` plugin is not enabled in `site.json`, all tagged elements will be rendered.
 
 **You can also use multiple tags in a single HTML element. Specify each tag in the `tags` attribute** separated by a space. An element will be rendered if **any of the tags** matches the one in `site.json`.
 
@@ -121,7 +128,14 @@ site.json
 
 {
   ...
-  "tags": ["-language--*", "language--C#"]
+  "plugins" : [
+    "filterTags"
+  ],
+  "pluginsContext" : {
+    "filterTags" : {
+      "tags": ["-language--*", "language--C#"]
+    }
+  }
 }
 ```
 

docs/userGuide/siteConfiguration.md

@@ -50,7 +50,14 @@ Here is a typical `site.json` file:
     "*.mbd",
     ".git/*"
   ],
-  "tags": ["tag1", "tag2"],
+  "plugins" : [
+    "filterTags"
+  ],
+  "pluginsContext" : {
+    "filterTags" : {
+      "tags": ["tag1", "tag2"]
+    }
+  },
   "headingIndexingLevel": 4
 }
 ```
@@ -164,9 +171,11 @@ The ignore pattern follows the [glob pattern used in .gitignore](https://git-scm
   The branch that will be deployed to in the remote repo.
 </div>
 
-#### **`tags`**
+#### **`plugins`**,  **`pluginsContext`**
+
+**A list of plugins to load.** Plugins are user-defined extensions that can add custom features to MarkBind. `pluginsContext` contains settings to be applied to the loaded plugins. See [User Guide: Using Plugins](usingPlugins.html) for more details.
 
-**A list of tags to filter page elements.**  Page elements with the specified tags are retained, while elements tagged with other tags are removed. Do not specify this option if you want to show everything. See [_User Guide: Tweaking the Page Structure → Using Tags_](tweakingThePageStructure.html#using-tags) section for more information.
+The example above uses tags as an example of configuring plugin settings, refer to the [`filterTags` plugin](tweakingThePageStructure.html#filtertags-toggling-alternative-contents-in-a-page) for more details.
 
 #### **`headingIndexingLevel`**