Install steps - Fixes syntax of `update_templates` django command

The command `rake django-admin[update_templates]`, mentioned in the installation instructions, didn't seem to work:

```
[edx-platform] antoviaque@antoviaque-laptop ~/prog/edx/edx-platform (master)
$ rake django-admin[update_templates]
django-admin.py update_templates --traceback --settings=lms.envs.dev --pythonpath=.
Unknown command: 'update_templates'
Type 'django-admin.py help' for usage.
rake aborted!
Command failed with status (1): [django-admin.py update_templates --traceba...]
[...]
Tasks: TOP => django-admin
(See full trace by running task with --trace)
```

Looking at the rakefiles, I saw `rake cms:update_templates`, which seemed to run fine for me (and both the LMS & CMS seemed to work fine afterwards) - not completely sure this is the same thing though: 

```
[edx-platform] antoviaque@antoviaque-laptop ~/prog/edx/edx-platform/rakefiles (master)
$ rake cms:update_templates
(in /home/antoviaque/prog/edx/edx-platform)
django-admin.py update_templates --traceback --settings=cms.envs.dev --pythonpath=.
2013-06-01 10:35:53,904 WARNING 9931 [xmodule.x_module] x_module.py:297 - No resource directory templates/customtag found when loading CustomTagDescriptor templates
2013-06-01 10:35:53,913 WARNING 9931 [xmodule.x_module] x_module.py:297 - No resource directory templates/poll found when loading PollDescriptor templates
2013-06-01 10:35:53,977 WARNING 9931 [xmodule.x_module] x_module.py:297 - No resource directory templates/foldit found when loading FolditDescriptor templates
2013-06-01 10:35:54,019 WARNING 9931 [xmodule.x_module] x_module.py:297 - No resource directory templates/abtest found when loading ABTestDescriptor templates
2013-06-01 10:35:55,171 WARNING 9931 [xmodule.x_module] x_module.py:297 - No resource directory templates/graphical_slider_tool found when loading GraphicalSliderToolDescriptor templates
```

(Also fixed a broken indentation, I can remove this part if needed, or isolate to a different patch.)