update interfaces

contracts/interfaces/IPriceFeed.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+/**
+ * @title IPriceFeed
+ * @notice 价格预言机接口
+ */
+interface IPriceFeed {
+    function getPrice() external view returns (uint256 price);
+    function decimals() external view returns (uint8);
+}
+