Restructure documentation. Now the documentation has installation, administration, usage, development, contributing the 5 main parts (#23629)

- **Installation**: includes how to install Gitea and related other
tools, also includes upgrade Gitea
- **Administration**: includes how to configure Gitea, customize Gitea
and manage Gitea instance out of Gitea admin UI
- **Usage**: includes how to use Gitea's functionalities. A sub
documentation is about packages, in future we could also include CI/CD
and others.
- **Development**: includes how to integrate with Gitea's API, how to
develop new features within Gitea
- **Contributing**: includes how to contribute code to Gitea
repositories.

After this is merged, I think we can have a sub-documentation of `Usage`
part named `Actions` to describe how to use Gitea actions

---------

Co-authored-by: John Olheiser <john.olheiser@gmail.com>

docs/content/doc/packages/npm.en-us.md

@@ -1,7 +1,7 @@
 ---
 date: "2021-07-20T00:00:00+00:00"
 title: "npm Packages Repository"
-slug: "packages/npm"
+slug: "usage/packages/npm"
 draft: false
 toc: false
 menu:
@@ -41,7 +41,7 @@ npm config set -- '//gitea.example.com/api/packages/{owner}/npm/:_authToken' "{t
 | ------------ | ----------- |
 | `scope`      | The scope of the packages. |
 | `owner`      | The owner of the package. |
-| `token`      | Your [personal access token]({{< relref "doc/developers/api-usage.en-us.md#authentication" >}}). |
+| `token`      | Your [personal access token]({{< relref "doc/development/api-usage.en-us.md#authentication" >}}). |
 
 For example: