Updated installation instructions.

Django 1.5 requires Python 2.6 or 2.7, and setup.py install over a
previous installation doesn't work.

INSTALL

@@ -1,17 +1,18 @@
 Thanks for downloading Django.
 
-To install it, make sure you have Python 2.5 or greater installed. Then run
+To install it, make sure you have Python 2.6 or greater installed. Then run
 this command from the command prompt:
 
     python setup.py install
 
+If you're upgrading from a previous version, you need to remove it first.
+
 AS AN ALTERNATIVE, you can just copy the entire "django" directory to Python's
 site-packages directory, which is located wherever your Python installation
 lives. Some places you might check are:
 
     /usr/lib/python2.7/site-packages (Unix, Python 2.7)
     /usr/lib/python2.6/site-packages (Unix, Python 2.6)
-    /usr/lib/python2.5/site-packages (Unix, Python 2.5)
     C:\\PYTHON\site-packages         (Windows)
 
 For more detailed instructions, see docs/intro/install.txt.