Various 3rd edition template improvements

- merge improvements from second edition (e.g. improved light switch, prefered theme in session storage, translation support)
- giscus instead of utterances
- add an alpha warning
- fix error caused by missing posts

etc

blog/content/edition-3/_index.md

@@ -1,3 +1,21 @@
 +++
 template = "edition-3/index.html"
 +++
+
+<h1>Writing an OS in Rust</h1>
+
+<h1 style="visibility: hidden; height: 0px; margin: 0px; padding: 0px;">Writing an OS in Rust</h1>
+
+<p>A blog by Philipp Oppermann <em class="gray">— Third Edition (Alpha Release)</em></p>
+
+<div class="front-page-introduction">
+
+This blog series creates a small operating system in the [Rust programming language](https://www.rust-lang.org/). Each post is a small tutorial and includes all needed code, so you can follow along if you like. The source code is also available in the corresponding [Github repository](https://github.com/phil-opp/blog_os).
+
+<!-- alpha-warning -->
+
+We explain how to create an operating system for the **`x86_64`** architecture step by step. Starting from scratch, we create a bootable OS kernel, implement basic input/output support, show how to test and debug our kernel, explain virtual memory management, and add support for multitasking and userspace programs.
+
+Latest post: <!-- latest-post -->
+
+</div>