Added Travis build status image.

Author: jezdez

README.rst

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 Django Debug Toolbar
 ====================
 
+.. image:: https://secure.travis-ci.org/django-debug-toolbar/django-debug-toolbar.png
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+    :target: http://travis-ci.org/django-debug-toolbar/django-debug-toolbar
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 The Django Debug Toolbar is a configurable set of panels that display various
 debug information about the current request/response and when clicked, display
 more details about the panel's content.