Added demo repository badge (#7915)

* docs(shortcodes): Add example repository badge

* docs(shortcodes): Update description for 'Example Repository'

* docs(relations): link example repos in docs pages

* docs(shortcodes): Fix permanent link for convention page

* docs(shortcodes): Revert to commit 365dc24

* docs(shortcodes): Rename md:example to md:demonstration

* docs(shortcodes): Fix examples url

* docs(shortcodes): Add demo badge

* docs(shortcodes): Add badges for demo repositories

* docs(shortcodes): Replace md:demonstration with md:example

* docs(shortcodes): Replace demonstration with example

* docs(shortcodes): Replace demonstration with example

* docs(shortcodes): Build new theme

* docs(shortcodes): Build with pymdownx

docs/setup/setting-up-a-blog.md

@@ -22,6 +22,7 @@ __Check out our [blog], which is created with the new [built-in blog plugin]!__
 <!-- md:version 9.2.0 -->
 <!-- md:plugin -->
 <!-- md:flag experimental -->
+<!-- md:demo create-blog -->
 
 The built-in blog plugin adds support for building a blog from a folder of
 posts, which are annotated with dates and other structured data. First, add the

docs/setup/setting-up-social-cards.md

@@ -37,6 +37,7 @@ Social card of our [formatting] reference
 <!-- md:version 8.5.0 -->
 <!-- md:plugin -->
 <!-- md:flag experimental -->
+<!-- md:demo create-social-cards -->
 
 The built-in social plugin automatically generate a custom preview image for
 each page. Install all [dependencies for image processing] and add the

docs/setup/setting-up-versioning.md

@@ -13,6 +13,7 @@ documentation remain untouched.
 
 <!-- md:version 7.0.0 -->
 <!-- md:utility [mike] -->
+<!-- md:demo example-versioning -->
 
 [mike] makes it easy to deploy multiple versions of your project documentation.
 It integrates natively with Material for MkDocs and can be enabled via