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

.config/shell/aliases

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+# Aliases used in all kinds of shells
+
+
+# Manage the bare `git` repository in ~/ holding the dotfiles
+alias dotfiles='git --git-dir=$DOTFILES_DIR --work-tree=$HOME'
+
+
+alias grep='grep --exclude-dir=.git'