Separated plugin documentation from extensions (#1390)

* Create minify-html.md

* Rename docs/minify-html.md to docs/plugins/minify-html.md

* Create search.md

* Update and rename docs/extensions/revision-date.md to docs/plugins/revision-date.md

* Update getting-started.md

* Update mkdocs.yml

docs/plugins/minify-html.md

@@ -0,0 +1,32 @@
+# Minify HTML
+
+[mkdocs-minify-plugin][1] is an extension that minifies HTML by stripping all whitespace from the generated documentation.
+
+  [1]: https://github.com/byrnereese/mkdocs-minify-plugin
+
+## Installation
+
+Install the plugin using `pip` with the following command:
+
+``` sh
+pip install mkdocs-minify-plugin
+```
+
+Next, add the following lines to your `mkdocs.yml`:
+
+``` yaml
+plugins:
+  - search
+  - minify:
+      minify_html: true
+```
+
+!!! warning "Remember to re-add the `search` plugin"
+
+    If you have no `plugins` entry in your config file yet, you'll likely also
+    want to add the `search` plugin. MkDocs enables it by default if there is
+    no `plugins` entry set.
+
+## Usage
+
+The output is automatically minified by the plugin.