feat: add 'aside' as a shortcode (#6)

The README has been updated to show a code example of both, including an
exemplary screenshot.

Since Hugo 0.55, we have to use `markdownify` in shortcodes that contain
HTML elements. At least we have to, if we want to render markdown code
inside the HTML element.

To use the `<aside>` element, we have to wrap our content in an
`<article>` tag.

This fixes #4.

Co-authored-by: Robert Lützner <robert.luetzner@iternity.com>

README.md

@@ -26,8 +26,30 @@ For more information on starting a Hugo website and using custom themes, refer t
 
 Freedom to Write has provided some awesome guides on writing HTML that works automatically with the formatting of Readable. For a complete HTML page guide on writing custom pages, see [Overall Structure](https://codeberg.org/Freedom-to-Write/readable.css/wiki/Overall-Structure). For some neat tips that may make life easier working with this style sheet, read [Quick Tips](https://codeberg.org/Freedom-to-Write/readable.css/wiki/Quick-Tips).
 
+## Shortcodes
+
+### aside
+
+readable.css prefers the `<aside>` HTML element over blockquotes. This theme supports both.
+
+```text
+> This is a blockquote.
+>
+> This is a default **markdown** element and supports formatting inside it.
+
+{{< aside >}}
+This is an aside element.
+
+You can use **markdown** formatting inside it.
+{{</ aside >}}
+```
+
+The above code generates the following output:
+
+![Comparing a blockquote to an aside. The blockquote has a thin bar on it's left, while the aside element is inside a nice box with rounded corners.](/docs/blockquote_vs_aside.png)
+
 ## Notes
 
 - Benjamin loves when new sites and projects pop up using the readable.css framework!
   - If you've built a complete site using this theme, submit an issue to the [original repo](https://codeberg.org/Freedom-to-Write/readable.css) with the URL of your site to be featured in the project's README.
-  - Projects like this and other non-website uses of the framework, such as adapting it to other static site generators, can be featured on the page [Unofficial Related Projects (that are awesome)](https://codeberg.org/Freedom-to-Write/readable.css/wiki/Unofficial-Related-Projects-%28that-are-awesome%29). Go mention [@freedomtowrite@fosstodon.org](https://fosstodon.org/@freedomtowrite) to be featured there!
+  - Projects like this and other non-website uses of the framework, such as adapting it to other static site generators, can be featured on the page [Unofficial Related Projects (that are awesome)](https://codeberg.org/Freedom-to-Write/readable.css/wiki/Unofficial-Related-Projects-%28that-are-awesome%29). Go mention [@freedomtowrite@fosstodon.org](https://fosstodon.org/@freedomtowrite) to be featured there!

layouts/_default/single.html

@@ -2,5 +2,7 @@
 <h1>{{ .Title }}</h1>
 {{ partial "metadata.html" . }}
 <!-- <br><br> -->
+<article>
 {{ .Content }}
-{{ end }}
+</article>
+{{ end }}

layouts/index.html

@@ -1,5 +1,7 @@
 {{ define "main" }}
 {{ partial "metadata.html" . }}
 <!-- <br><br> -->
+<article>
 {{ .Content }}
-{{ end }}
+</article>
+{{ end }}

layouts/shortcodes/aside.html

@@ -0,0 +1 @@
+<aside>{{ .Inner | markdownify }}</aside>