minor #701 [WIP] Adding a quick note explaining paramters.yml.dist a little (weaverryan)

This PR was squashed before being merged into the 2.3 branch (closes #701).

Discussion
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[WIP] Adding a quick note explaining paramters.yml.dist a little

Hi guys!

This is really simple, but a WIP because I also want to add an additional link at the top to symfony/symfony-docs#4174 after it's created.

Thanks!

Commits
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2f58ce7 [WIP] Adding a quick note explaining paramters.yml.dist a little

Author: fabpot

app/config/parameters.yml.dist

@@ -1,3 +1,4 @@
+# This file is a "template" of what your parameters.yml file should look like
 parameters:
     database_driver:   pdo_mysql
     database_host:     127.0.0.1
@@ -14,4 +15,6 @@ parameters:
     mailer_password:   ~
 
     locale:            en
+
+    # A secret key that's used to generate certain security-related tokens
     secret:            ThisTokenIsNotSoSecretChangeIt