update examples and sphnix docs for the new api (#63)

docs/config.md

@@ -18,6 +18,15 @@ fp16 = dict(
     initial_scale=2 ** 8
 )
 
+# optional
+# configuration for zero
+# you can refer to the Zero Redundancy optimizer and zero offload section for details
+# https://www.colossalai.org/zero.html
+zero = dict(
+    level=<int>,
+    ...
+)
+
 # optional
 # if you are using complex gradient handling
 # otherwise, you do not need this in your config file