docs: wrote part of new usage section

docs/content/usage/_index.md

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+# Usage
+
+This section describes how to use the various parts of Vieter. It assumes you
+have a Vieter repository server up and running.

docs/content/usage/repository.md

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+# Pacman repository
+
+The part of Vieter that users will interact with the most is the Pacman
+repository aka `vieter server`.
+
+## Design overview
+
+A Vieter repository server has support for multiple repositories, with each
+repository containing packages for multiple architectures.
+
+If you wish to use these repositories on your system, add the following to
+`/etc/pacman.conf` for each repository you wish to use:
+
+```
+[repo-name]
+Server = https://example.com/$repo/$arch
+SigLevel = Optional
+```
+
+Here, `$repo` & `$arch` are not variables you have to fill in yourself. Rather,
+Pacman will substitute these when reading the config file. `$repo` is replaced
+by the name between the square brackets (in this case `repo-name`), & `$arch`
+is replaced by your system's architecture, e.g. `x86_64`. Of course, you can
+also fill in these values manually yourself, e.g. if you wish to use a
+different name inside the square brackets.
+
+Important to note is that, when two repositories contain a package with the
+same name, Pacman will choose the one from the repository that's highest up in
+the `pacman.conf` file. Therefore, if you know your repository has packages
+with the same name as ones from the official repositories, it might be better
+to place the repository below the official repositories to avoid overwriting
+official packages.
+
+## Publishing packages
+
+Packages can be easily published using a single HTTP POST request. Check out
+the [HTTP API docs](https://rustybever.be/docs/vieter/api/) for more info on
+these routes, including example cURL commands.

docs/content/usage/usage.md

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+---
+weight: 30
+---
+# Usage
+
+## Starting the server
+
+To start a server, either install it using Docker (see
+[Installation](/installation)) or run it locally by executing `vieter
+server`. See [Configuration](/configuration) for more information about
+configuring the binary.
+
+## Multiple repositories
+
+Vieter works with multiple repositories. This means that a single Vieter server
+can serve multiple repositories in Pacman. It also automatically divides files
+with specific architectures among arch-repos. Arch-repos are the actual
+repositories you add to your `/etc/pacman.conf` file. See [Configuring
+Pacman](/usage#configuring-pacman) below for more info.
+
+## Adding packages
+
+Using Vieter is currently very simple. If you wish to add a package to Vieter,
+build it using makepkg & POST that file to the `/<repo>/publish` endpoint of
+your server. This will add the package to the repository. Authentification
+requires you to add the API key as the `X-Api-Key` header.
+
+All of this can be combined into a simple cURL call:
+
+```
+curl -XPOST -H "X-API-KEY: your-key" -T some-package.pkg.tar.zst https://example.com/somerepo/publish
+```
+
+`somerepo` is automatically created if it doesn't exist yet.
+
+## Configuring Pacman
+
+Configuring Pacman to use a Vieter instance is very simple. In your
+`/etc/pacman.conf` file, add the following lines:
+
+```
+[vieter]
+Server = https://example.com/$repo/$arch
+SigLevel = Optional
+```
+
+Here, you see two important placeholder variables. `$repo` is replaced by the
+name within the square brackets, which in this case would be `vieter`. `$arch`
+is replaced by the output of `uname -m`. Because Vieter supports multiple
+repositories & architectures per repository, using this notation makes sure you
+always use the correct endpoint for fetching files.
+
+I recommend placing this below all other repository entries, as the order
+decides which repository should be used if there's ever a naming conflict.