Add base configuration

- Follow XDG standard: ~/.config and ~/.local folders
- Set environment variables and define aliases within ~/.config/shell
- Add installation script for easy setup and maintenance
  (i.e., `install-dotfiles` and `update-dotfiles`,
   and a `ensure-locales` helper)
- Add README.md with info on the installation and general notes

README.md

@@ -0,0 +1,61 @@
+# Dotfiles
+
+This repository contains useful (config) files.
+
+There are two branches:
+- [*main*](https://code.webartifex.de/alexander/dotfiles/src/branch/main) (~ "headless")
+- [*desktop*](https://code.webartifex.de/alexander/dotfiles/src/branch/desktop) (for GNOME 48+ on X11)
+
+`main` contains dotfiles intended to be used on all kinds of machines
+    and can be thought of as a "minimal" or "server" version.
+It targets [Debian](https://www.debian.org/) 13
+    but is kept working on older versions and other distributions as well.
+`desktop` is (re-)based on top of `main`
+    and adds configurations for
+    [GNOME](https://www.gnome.org/) 48+
+    on [X11](https://www.x.org/)
+    and many applications,
+    be it end-user software or common development utilities.
+
+
+## Installation
+
+Simply run:
+
+```sh
+curl https://code.webartifex.de/alexander/dotfiles/raw/branch/main/.local/bin/dotfiles-install > dotfiles-install && sh ./dotfiles-install && rm ./dotfiles-install
+```
+
+or
+
+```sh
+wget https://code.webartifex.de/alexander/dotfiles/raw/branch/main/.local/bin/dotfiles-install -O dotfiles-install && sh ./dotfiles-install && rm ./dotfiles-install
+```
+
+This downloads a simple [installation script](.local/bin/dotfiles-install)
+    and then executes it.
+The script's only dependency is [`git`](https://git-scm.com/).
+So, it should not be too hard to get this going.
+
+The repository is cloned as a bare repository into `~/.local/share/dotfiles`
+    and its files are checked out into `~/` directly.
+Pre-existing files are backed up to `~/.local/state/dotfiles-backups` beforehand.
+Afterwards, the files can be managed with the
+    [`dotfiles`](.config/shell/aliases#L7) alias,
+    for example, `dotfiles status` or `dotfiles pull`.
+
+The above commands install the *main* variant.
+To install the *desktop* variant,
+    switch to the [desktop](https://code.webartifex.de/alexander/dotfiles/src/branch/desktop) branch first.
+
+Normally, I advise against executing shell scripts from the internet,
+    but this one is short enough to be read even by beginners.
+So, convince yourself that it is not harmful!
+
+
+## Shells
+
+The config files in this repository are optimized for usage with
+    [GNU's Bourne again shell](https://man7.org/linux/man-pages/man1/bash.1.html),
+    or `bash` for short,
+    and the popular [zsh](https://www.zsh.org/).