Add some doc strings.

Author: chawco

pyres/failure/multiple.py

@@ -2,6 +2,25 @@
 from redis import RedisBackend
 
 class MultipleBackend(BaseBackend):
+    """Extends ``BaseBackend`` to provide support for delegating calls to multiple
+    backends. Queries are delegated to the first backend in the list. Defaults to
+    only the RedisBackend.
+
+    To use:
+
+    from pyres import failure
+
+    from pyres.failure.base import BaseBackend
+    from pyres.failure.multiple import MultipleBackend
+    from pyres.failure.redis import RedisBackend
+
+    class CustomBackend(BaseBackend):
+        def save(self, resq):
+            print('Custom backend')
+
+            failure.backend = MultipleBackend
+            failure.backend.classes = [RedisBackend, CustomBackend]
+    """
     classes = []
 
     def __init__(self, *args):