Added note about exporting SYMFONY_ENV
feature #4182 Added note about exporting SYMFONY_ENV (jpb0104)

This PR was merged into the 2.3 branch.

Discussion
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Added note about exporting SYMFONY_ENV

New PR to replace the mess I made in #4001. Sorry about that. I also applied all the suggestions.

Commits
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15ce0fe Added note about exporting SYMFONY_ENV