Create skeleton for new post about threads

blog/content/second-edition/posts/12-threads/index.md

@@ -0,0 +1,42 @@
++++
+title = "Threads"
+weight = 12
+path = "threads"
+date = 0000-01-01
+
+[extra]
+chapter = "Multitasking"
++++
+
+TODO
+
+<!-- more -->
+
+This blog is openly developed on [GitHub]. If you have any problems or questions, please open an issue there. You can also leave comments [at the bottom]. The complete source code for this post can be found in the [`post-12`][post branch] branch.
+
+[GitHub]: https://github.com/phil-opp/blog_os
+[at the bottom]: #comments
+[post branch]: https://github.com/phil-opp/blog_os/tree/post-12
+
+<!-- toc -->
+
+## Introduction
+
+### Multitasking
+
+## Thread Creation
+
+### Stack Allocation
+
+## Switching Stacks
+
+## Saving Registers
+
+## Scheduler
+
+## Summary
+TODO
+
+## What's next?
+
+TODO