Add per-file-ignores mention in violations.rst

docs/source/user/violations.rst

@@ -136,6 +136,38 @@ the errors in that file will show up without having to modify our
 configuration. Both exist so we can choose which is better for us.
 
 
+Ignoring Violations in Specific Files
+-------------------------------------
+
+If we want to ignore one or more violation codes for certain files, you can
+use the :option:`flake8 --per-file-ignores` on either the command-line
+or in your configuration file.
+
+.. prompt:: bash
+
+   flake8 --per-file-ignores='project/test.py:F841 setup.py:E121'
+   flake8 --per-file-ignores='tests/*:F841,D setup.py:E121'
+
+.. note::
+
+   While most options in Flake8 use commas to separate values, this option allows
+   multiple violation codes to be specified per file with commas so to specify
+   multiple file mappings use spaces to delimit them.
+
+We can also specify it in config file:
+
+.. code-block:: ini
+
+     per-file-ignores =
+            project/test.py:F841
+            tests/*:F841,D
+            setup.py:E121
+            other_project/*:W9
+
+Syntax is similar with :option:`flake8 --exclude` for files
+and :option:`flake8 --ignore` for errors.
+
+
 
 Selecting Violations with Flake8
 ================================