Feature/brief doc (#112)

* auction, oracle and prices brief documentation

* add gradually-update and schedule-update brief doc

Co-authored-by: Ermal Kaleci <ermalkaleci@gmail.com>

gradually-update/README.md

+# Gradually-update module
+
+### Overview
+
+Gradually-update module provides a way to adjust numeric parameter such as stability fee or liquidation gradually. The update code should be able to handle different numeric types such as `u32`, `u128`, `Permill`, `FixedU128`. All the values are assumed to be little-endian and unsigned.

schedule-update/README.md

+# Schedule-update module
+
+### Overview
+
+Schedule-update module provides a way to allow an update to be dispatched at later block. This is Useful for council to dispatch a delayed update so other have time to review and learn the change. Council also have chance to cancel the update if any issues were found.