Add install instructions.

doc/changelog.txt

@@ -2,6 +2,7 @@
 
   * Print help when unknown options are given.
   * Print error when archive files do not exist.
+  * Added installation instructions in doc/install.txt
 
 0.14 "Book of Dragons" (released 30.1.2012)
 

doc/install.txt

@@ -0,0 +1,37 @@
+Installation
+============
+
+First, install the required software.
+
+1. Python >= 2.7 from http://www.python.org/
+   
+   Be sure to also have installed the included distutils module.
+   On most distributions, the distutils module is included in
+   an extra ``python-dev`` package.
+
+
+Now install the application.
+
+1.
+   a) Installation as root
+      
+      Run ``sudo python setup.py install`` to install patool.
+   
+   b) Installation as a normal user
+      
+      Run ``python setup.py install --home $HOME``. Note that you have
+      to adjust your PATH and PYTHONPATH environment variables, eg. by
+      adding the commands ``export PYTHONPATH=$HOME/lib/python`` and
+      ``export PATH=$PATH:$HOME/bin`` to your shell configuration
+      file.
+      
+      For more information look at the `Modifying Python's search path`_
+      documentation.
+      
+      .. _Modifying Python's search path:
+         http://docs.python.org/inst/search-path.html#SECTION000410000000000000000
+
+
+After installation
+------------------
+Patool is now installed. Have fun!