Updated docs/topics/install.txt to note github URL instead of code.djangoproject.com

If you'd like to be able to update your Django code occasionally with the

latest bug fixes and improvements, follow these instructions:

1. Make sure that you have Subversion_, Git_, or Mercurial_ installed, and

   that you can run its commands from a shell. (Enter ``svn help``,

   ``git help``, or ``hg help`` at a shell prompt to test this.) Note that

   the Subversion repository is the canonical source for the official

   Git and Mercurial repositories and as such will always be the most up-to-date.

1. Make sure that you have Git_ installed and that you can run its commands

   from a shell. (Enter ``git help`` at a shell prompt to test this.)

2. Check out Django's main development branch (the 'trunk') like so:

2. Check out Django's main development branch (the 'trunk' or 'master') like

   so:

   .. code-block:: bash

       # Subversion

       svn co https://code.djangoproject.com/svn/django/trunk/ django-trunk

       git clone git://github.com/django/django.git django-trunk

   Mirrors of the Subversion repository can be obtained like so:

   .. code-block:: bash

       # Git (requires version 1.6.6 or later)

       git clone https://github.com/django/django.git

       # or (works with all versions)

       git clone git://github.com/django/django.git

       # Mercurial

       hg clone https://bitbucket.org/django/django

   .. warning ::

        These mirrors should be updated every 5 minutes but aren't guaranteed

        to be up-to-date since they are hosted on external services.

   This will create a directory ``django-trunk`` in your current directory.

3. Next, make sure that the Python interpreter can load Django's code. The most

   convenient way to do this is to `modify Python's search path`_. Add a ``.pth``

    known to cause problems when updating to a more recent version of Django.

When you want to update your copy of the Django source code, just run the

command ``svn update`` from within the ``django-trunk`` directory. When you do

this, Subversion will automatically download any changes. The equivalent

command for Git is ``git pull``, and for Mercurial ``hg pull --update``.

command ``git pull`` from within the ``django-trunk`` directory. When you do

this, Git will automatically download any changes.

.. _Subversion: http://subversion.tigris.org/

.. _Git: http://git-scm.com/

.. _Mercurial: http://mercurial.selenic.com/

.. _`modify Python's search path`: http://docs.python.org/install/index.html#modifying-python-s-search-path