minor #824 [README] Add DebugBundle to the list (edvinasme)

This PR was squashed before being merged into the 2.6 branch (closes #824).

Discussion
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[README] Add DebugBundle to the list

| Q             | A
| ------------- | ---
| Bug fix?      | [no]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets |
| License       | MIT
| Doc PR        |

This commits mentions **DebugBundle** in the readme. I believe this should also be ported to 2.7, 2.8 and master branches.

Have a nice weekend!

Commits
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b557e01 [README] Add DebugBundle to the list

Author: fabpot

README.md

@@ -53,6 +53,9 @@ It comes pre-configured with the following bundles:
   * [**SensioGeneratorBundle**][13] (in dev/test env) - Adds code generation
     capabilities
 
+  * **DebugBundle** (in dev/test env) - Adds Debug and VarDumper component
+    integration
+
 All libraries and bundles included in the Symfony Standard Edition are
 released under the MIT or BSD license.