Added documentation about new requests formats configuration
feature #3402 Added documentation about new requests formats configuration (gquemener)

This PR was merged into the master branch.

Discussion
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Added documentation about new requests formats configuration

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes (https://github.com/symfony/symfony/pull/9862)
| Applies to    | 2.5
| Fixed tickets | https://github.com/symfony/symfony/issues/8934

Commits
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6adf160 Added documentation about new requests formats configuration