Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/token/ERC20/extensions/IERC20Metadata.sol

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)
+
+pragma solidity ^0.8.0;
+
+import "../IERC20.sol";
+
+/**
+ * @dev Interface for the optional metadata functions from the ERC20 standard.
+ *
+ * _Available since v4.1._
+ */
+interface IERC20Metadata is IERC20 {
+    /**
+     * @dev Returns the name of the token.
+     */
+    function name() external view returns (string memory);
+
+    /**
+     * @dev Returns the symbol of the token.
+     */
+    function symbol() external view returns (string memory);
+
+    /**
+     * @dev Returns the decimals places of the token.
+     */
+    function decimals() external view returns (uint8);
+}