minor #7801 Added a new article about linting translation files (javiereguiluz)

This PR was merged into the 2.7 branch.

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Added a new article about linting translation files

This continues #7618 with a simpler article aimed at 2.7 -> 3.2. **Don't merge it up to master** because there's a more complete version of this article.

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bd97f70 Added a new article about linting translation files

Author: xabbuh

translation/lint.rst

@@ -0,0 +1,31 @@
+.. 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 translation file
+using the ``lint:yaml`` command:
+
+.. code-block:: terminal
+
+    # lint a single file
+    $ ./bin/console lint:yaml app/Resources/translations/messages.en.yml
+
+    # lint a whole directory
+    $ ./bin/console lint:yaml app/Resources/translations
+
+    # lint a specific bundle
+    $ ./bin/console lint:yaml @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