chore(jellyfin): start adding notes

knowledge base/jellyfin.md

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+# Jellyfin
+
+Free software media system.<br/>
+Allows streaming to any device from one's own server, with no strings attached.
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+   1. [Sources](#sources)
+
+## TL;DR
+
+TODO
+
+<!-- Uncomment if used
+<details>
+  <summary>Setup</summary>
+
+```sh
+```
+
+</details>
+-->
+
+<!-- Uncomment if used
+<details>
+  <summary>Usage</summary>
+
+```sh
+```
+
+</details>
+-->
+
+<!-- Uncomment if used
+<details>
+  <summary>Real world use cases</summary>
+
+```sh
+```
+
+</details>
+-->
+
+## Further readings
+
+- [Website]
+- [Codebase]
+- [Blog]
+
+### Sources
+
+- [Documentation]
+
+<!--
+  Reference
+  ═╬═Time══
+  -->
+
+<!-- In-article sections -->
+<!-- Knowledge base -->
+<!-- Files -->
+<!-- Upstream -->
+[Blog]: https://jellyfin.org/posts
+[Codebase]: https://github.com/jellyfin/jellyfin
+[Documentation]: https://jellyfin.org/docs
+[Website]: https://jellyfin.org/
+
+<!-- Others -->