minor #7306 Improved the image for Doctrine + Web Debug Toolbar (javiereguiluz)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #7306).

Discussion
----------

Improved the image for Doctrine + Web Debug Toolbar

This fixes #7301. The image file renaming is recommended because all images from the Symfony Docs are flattened in a single `_images/` directory. We should start "namespacing" image file names to avoid collisions.

### Before

![before_image](https://cloud.githubusercontent.com/assets/73419/21587282/a6cd3478-d0da-11e6-87a3-77fb4da51bcd.png)

### After

![after_image](https://cloud.githubusercontent.com/assets/73419/21587284/a9776ee6-d0da-11e6-8ffb-cc00078d10a4.png)

Commits
-------

a01e522 Improved the image for Doctrine + Web Debug Toolbar

Author: xabbuh

_images/doctrine/doctrine_web_debug_toolbar.png

@@ -662,19 +662,17 @@ to easily fetch objects based on multiple conditions::
 
 .. tip::
 
-    When you render any page, you can see how many queries were made in the
-    bottom right corner of the web debug toolbar.
+    When rendering a page requires to make some database calls, the web debug
+    toolbar at the bottom of the page displays the number of queries and the
+    time it took to execute them:
 
-    .. image:: /_images/doctrine/web_debug_toolbar.png
+    .. image:: /_images/doctrine/doctrine_web_debug_toolbar.png
        :align: center
-       :scale: 50
-       :width: 350
+       :class: with-browser
 
-    If you click the icon, the profiler will open, showing you the exact
-    queries that were made.
-
-    The icon will turn yellow if there were more than 50 queries on the
-    page. This could indicate that something is not correct.
+    If the number of database queries is too high, the icon will turn yellow to
+    indicate that something may not be correct. Click on the icon to open the
+    Symfony Profiler and see the exact queries that were executed.
 
 Updating an Object
 ~~~~~~~~~~~~~~~~~~