Update installation instructions

README.org

@@ -16,5 +16,40 @@
 
 ** Installation
 
-   To install place it somewhere in your ~custom-theme-load-path~ and
-   then ~load-theme~.
+   Installation comes in two flavors.
+
+*** Installation with ELPA
+
+    To install Yoshi theme using the built-in Emacs package manager
+    you should have [[https://marmalade-repo.org/][Marmalade]] in your =package-archives= list. When
+    that's ready you can =M-x list-packages=, find =yoshi-theme=, press =i=
+    and =x= and you're done.
+
+*** Installation from git
+
+    To use a version from the latest git checkout you should clone the
+    repository and then add the directory to your
+    =custom-theme-load-path=.
+
+    In a shell execute:
+
+    #+BEGIN_EXAMPLE
+    cd ~/
+    git clone git://github.com/ryuslash/yoshi-theme.git
+    #+END_EXAMPLE
+
+    Then add to your =~/.emacs.d/init.el=:
+
+    #+BEGIN_SRC emacs-lisp
+      (add-to-list 'custom-theme-load-path (expand-file-name "~/yoshi-theme"))
+    #+END_SRC
+
+** Enabling Yoshi theme
+
+   Once you've installed Yoshi theme you can either use =M-x
+   load-theme= to enable it interactively for the current session, or
+   put the following in your =~/.emacs.d/init.el=:
+
+   #+BEGIN_SRC emacs-lisp
+     (load-theme 'yoshi :no-confirm)
+   #+END_SRC