Update README.rst

Author: gnikonorov

README.rst

@@ -55,6 +55,24 @@ test re-run is launched:
 
    $ pytest --reruns 5 --reruns-delay 1
 
+Re-run all failures matching certain expressions
+------------------------------------------------
+
+To re-run only those failures that match a certain list of expressions, use the
+``--only-rerun`` flag and pass it a regular expression. For example, the following would
+only rerun those errors that match ``AssertionError``:
+
+.. code-block:: bash
+
+   $ pytest --reruns 5 --only-rerun AssertionError
+   
+Passing the flag multiple times accumulates the arguments, so the following would only rerun
+those errors that match ``AssertionError`` or ``ValueError``:
+
+.. code-block:: bash
+
+   $ pytest --reruns 5 --only-rerun AssertionError --only-rerun ValueError
+
 Re-run individual failures
 --------------------------