minor #402 Add note about deploying dev environment to Heroku (bocharsky-bw, javiereguiluz)

This PR was merged into the master branch.

Discussion
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Add note about deploying dev environment to Heroku

According to the #398

Commits
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00259b7 Tweaked the warning message
5113ee5 Add note about deploying dev environment to Heroku

Author: javiereguiluz

app.json

@@ -13,7 +13,10 @@
         "postdeploy": "php bin/console doctrine:schema:create && php bin/console doctrine:fixtures:load -n"
     },
     "env": {
-        "SYMFONY_ENV": "prod",
+        "SYMFONY_ENV": {
+            "value": "prod",
+            "description": "If you want to use the Symfony `dev` environment in the deployed application, you must move the necessary dependencies (like SensioGeneratorBundle) from `require-dev` to `require`. This will introduce security issues because development tools like the WebProfiler reveal sensitive information."
+        },
         "SYMFONY_LOG": "php://stderr",
         "SYMFONY_SECRET": {
             "description": "Extra entropy for %kernel.secret%; used for CSRF tokens, cookies and signed URLs.",