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/administration/cmd-embedded.en-us.md

@@ -0,0 +1,121 @@
+---
+date: "2020-01-25T21:00:00-03:00"
+title: "Embedded data extraction tool"
+slug: "cmd-embedded"
+weight: 40
+toc: false
+draft: false
+menu:
+  sidebar:
+    parent: "administration"
+    name: "Embedded data extraction tool"
+    weight: 20
+    identifier: "cmd-embedded"
+---
+
+# Embedded data extraction tool
+
+**Table of Contents**
+
+{{< toc >}}
+
+Gitea's executable contains all the resources required to run: templates, images, style-sheets
+and translations. Any of them can be overridden by placing a replacement in a matching path
+inside the `custom` directory (see [Customizing Gitea]({{< relref "doc/administration/customizing-gitea.en-us.md" >}})).
+
+To obtain a copy of the embedded resources ready for editing, the `embedded` command from the CLI
+can be used from the OS shell interface.
+
+**NOTE:** The embedded data extraction tool is included in Gitea versions 1.12 and above.
+
+## Listing resources
+
+To list resources embedded in Gitea's executable, use the following syntax:
+
+```sh
+gitea embedded list [--include-vendored] [patterns...]
+```
+
+The `--include-vendored` flag makes the command include vendored files, which are
+normally excluded; that is, files from external libraries that are required for Gitea
+(e.g. [font-awesome](https://fontawesome.com/), [octicons](https://octicons.github.com/), etc).
+
+A list of file search patterns can be provided. Gitea uses [gobwas/glob](https://github.com/gobwas/glob)
+for its glob syntax. Here are some examples:
+
+- List all template files, in any virtual directory: `**.tmpl`
+- List all mail template files: `templates/mail/**.tmpl`
+- List all files inside `public/img`: `public/img/**`
+
+Don't forget to use quotes for the patterns, as spaces, `*` and other characters might have
+a special meaning for your command shell.
+
+If no pattern is provided, all files are listed.
+
+### Example
+
+Listing all embedded files with `openid` in their path:
+
+```sh
+$ gitea embedded list '**openid**'
+public/img/auth/openid_connect.svg
+public/img/openid-16x16.png
+templates/user/auth/finalize_openid.tmpl
+templates/user/auth/signin_openid.tmpl
+templates/user/auth/signup_openid_connect.tmpl
+templates/user/auth/signup_openid_navbar.tmpl
+templates/user/auth/signup_openid_register.tmpl
+templates/user/settings/security_openid.tmpl
+```
+
+## Extracting resources
+
+To extract resources embedded in Gitea's executable, use the following syntax:
+
+```sh
+gitea [--config {file}] embedded extract [--destination {dir}|--custom] [--overwrite|--rename] [--include-vendored] {patterns...}
+```
+
+The `--config` option tells Gitea the location of the `app.ini` configuration file if
+it's not in its default location. This option is only used with the `--custom` flag.
+
+The `--destination` option tells Gitea the directory where the files must be extracted to.
+The default is the current directory.
+
+The `--custom` flag tells Gitea to extract the files directly into the `custom` directory.
+For this to work, the command needs to know the location of the `app.ini` configuration
+file (`--config`) and, depending of the configuration, be ran from the directory where
+Gitea normally starts. See [Customizing Gitea]({{< relref "doc/administration/customizing-gitea.en-us.md" >}}) for details.
+
+The `--overwrite` flag allows any existing files in the destination directory to be overwritten.
+
+The `--rename` flag tells Gitea to rename any existing files in the destination directory
+as `filename.bak`. Previous `.bak` files are overwritten.
+
+At least one file search pattern must be provided; see `list` subcomand above for pattern
+syntax and examples.
+
+### Important notice
+
+Make sure to **only extract those files that require customization**. Files that
+are present in the `custom` directory are not upgraded by Gitea's upgrade process.
+When Gitea is upgraded to a new version (by replacing the executable), many of the
+embedded files will suffer changes. Gitea will honor and use any files found
+in the `custom` directory, even if they are old and incompatible.
+
+### Example
+
+Extracting mail templates to a temporary directory:
+
+```sh
+$ mkdir tempdir
+$ gitea embedded extract --destination tempdir 'templates/mail/**.tmpl'
+Extracting to tempdir:
+tempdir/templates/mail/auth/activate.tmpl
+tempdir/templates/mail/auth/activate_email.tmpl
+tempdir/templates/mail/auth/register_notify.tmpl
+tempdir/templates/mail/auth/reset_passwd.tmpl
+tempdir/templates/mail/issue/assigned.tmpl
+tempdir/templates/mail/issue/default.tmpl
+tempdir/templates/mail/notify/collaborator.tmpl
+```