Add very basic use-package tutorial.

doc/VIMUSERS.org

@@ -303,3 +303,46 @@ pattern as packages.
 
 Make sure you [[*Activating%20a%20Layer][add]] your layer to your =.dotspacemacs= file and restart to
 activate it.
+** Installing a single package
+Sometimes creating a layer is a bit overkill. Maybe you just want one package
+and don't want to maintain a whole layer. Spacemacs provides a variable in the
+=dotspacemacs/init= function in =.spacemacs= called
+=dotspacemacs-additional-packages=. Just add a package name to the list and it
+will be installed when you restart. Loading the package is covered in the next [[*Loading%20packages][section.]]
+
+** Loading packages
+Ever wonder how Spacemacs can load over a 100 packages in just a few seconds?
+Such low loading times must require some kind of unreadable black magic that no
+one can understand. Thanks to [[https://github.com/jwiegley/use-package][use-package]], this is not true. It is a package
+that allows easy lazy-loading and configuration of packages. Here are the basics
+to using it:
+
+#+begin_src emacs-lisp
+  ;; Basic form of use-package declaration.
+  ;; The :defer t tells use-package to try to lazy load the package.
+  (use-package package-name
+    :defer t)
+  ;; The :init section is run before the package loads
+  ;; The :config section is run after the package loads
+  (use-package package-name
+    :defer t
+    :init
+    (progn
+      ;; Change some variables
+      (setq variable1 t
+            variable2 nil)
+      ;; Define a function
+      (defun foo ()
+        (message "%s" "Hello, World!")))
+    :config
+    (progn
+      ;; Calling a function that is defined when the package loads
+      (function-defined-when-package-loads)))
+#+end_src
+
+This is just a very basic overview of =use-package=. There are many other ways
+to control how a package loads using it that aren't covered here.
+** Common tweaks
+This section is for things almost everyone will want to change. All of these
+settings go in the =dotspacemacs/config= function in your =.spacemacs= unless
+otherwise noted.