minor #77 Proofing the controller chapter (weaverryan)

This PR was squashed before being merged into the 2.7 branch (closes #77).

Discussion
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Proofing the controller chapter

Removing a lot of duplication between this and routing - which is tricky because they
are quite related topics.

See #72

Commits
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8afcade Proofing the controller chapter

Author: javiereguiluz

configuration.rst

@@ -182,6 +182,8 @@ The ``imports`` key works a lot like the PHP ``include`` function: the contents
 ``parameters.yml``, ``security.yml`` and ``services.yml`` are read and loaded. You
 can also load XML files or PHP files.
 
+.. _config-parameter-intro:
+
 The parameters key: Parameters (Variables)
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