feature #7618 Added a new short article about linting translation files (javiereguiluz)

This PR was squashed before being merged into the master branch (closes #7618).

Discussion
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Added a new short article about linting translation files

This fixes #7536.

Commits
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df7841b Added a new short article about linting translation files

Author: xabbuh

translation/lint.rst

@@ -0,0 +1,35 @@
+.. index::
+    single: Translation; Lint
+    single: Translation; Translation File Errors
+
+How to Find Errors in Translation Files
+=======================================
+
+Symfony processes all the application translation files as part of the process
+that compiles the application code before executing it. If there's an error in
+any translation file, you'll see an error message explaining the problem.
+
+If you prefer, you can also validate the contents of any YAML and XLIFF
+translation file using the ``lint:yaml`` and ``lint:xliff`` commands:
+
+.. code-block:: terminal
+
+    # lint a single file
+    $ ./bin/console lint:yaml app/Resources/translations/messages.en.yml
+    $ ./bin/console lint:xliff app/Resources/translations/messages.en.xlf
+
+    # lint a whole directory
+    $ ./bin/console lint:yaml app/Resources/translations
+    $ ./bin/console lint:xliff app/Resources/translations
+
+    # lint a specific bundle
+    $ ./bin/console lint:yaml @AppBundle
+    $ ./bin/console lint:xliff @AppBundle
+
+The linter results can be exported to JSON using the ``--format`` option:
+
+.. code-block:: terminal
+
+    # lint a single file
+    $ ./bin/console lint:yaml app/Resources/translations --format=json
+    $ ./bin/console lint:xliff app/Resources/translations --format=json