Docusaurus-ify (#26051)

This PR cleans up the docs in a way to make them simpler to ingest by
our [docs repo](https://gitea.com/gitea/gitea-docusaurus).

1. It includes all of the sed invocations our ingestion did, removing
the need to do it at build time.
2. It replaces the shortcode variable replacement method with
`@variable@` style, simply for easier sed invocations when required.
3. It removes unused files and moves the docs up a level as cleanup.

---------

Signed-off-by: jolheiser <john.olheiser@gmail.com>

docs/content/contributing/localization.en-us.md

@@ -0,0 +1,39 @@
+---
+date: "2016-12-01T16:00:00+02:00"
+title: "Localization"
+slug: "localization"
+sidebar_position: 70
+toc: false
+draft: false
+aliases:
+  - /en-us/localization
+menu:
+  sidebar:
+    parent: "contributing"
+    name: "Localization"
+    sidebar_position: 70
+    identifier: "localization"
+---
+
+# Localization
+
+Gitea's localization happens through our [Crowdin project](https://crowdin.com/project/gitea).
+
+For changes to an **English** translation, a pull request can be made that changes the appropriate key in
+the [english locale](https://github.com/go-gitea/gitea/blob/main/options/locale/locale_en-US.ini).
+
+For changes to a **non-English** translation, refer to the Crowdin project above.
+
+## Supported Languages
+
+Any language listed in the above Crowdin project will be supported as long as 25% or more has been translated.
+
+After a translation has been accepted, it will be reflected in the main repository after the next Crowdin sync, which is generally after any PR is merged.
+
+At the time of writing, this means that a changed translation may not appear until the following Gitea release.
+
+If you use a bleeding edge build, it should appear as soon as you update after the change is synced.
+
+# How to Contribute
+
+Different Languages have different translation guidelines. Please visit the respective page for more information.