Add custom ERC20 functions

docs/build/isc/v1.0.0-rc.6/docs/how-tos/token/erc20-native-token.md

@@ -0,0 +1,40 @@
+---
+description: How to use the custom functionality of ERC20NativeToken
+image: /img/logo/WASP_logo_dark.png
+tags:
+  - native token
+  - erc20
+  - EVM
+  - how-to
+---
+
+# Custom ERC20 functions
+
+Once you [registered your native token as ERC20](./erc20-native-token.md) you can basically use it like any other ERC20 token, with functions like `transfer`, `balanceOf` and so on. But as the ERC20 token maps the native token on L2 there are some additional fetures.
+
+## Example Code
+
+1. Get your `ERC20NativeTokens` instance (In this case we will use `erc20NativeTokensAddress` and the Foundry serial number to get the contract address)
+```solidity
+        ERC20NativeTokens token = ERC20NativeTokens(
+            ISC.sandbox.erc20NativeTokensAddress(_foundrySN)
+        );
+```
+
+* `nativeTokenID` will give you the native token ID of the ERC20 token
+```solidity
+        NativeTokenID memory id =token.nativeTokenID();
+```
+
+
+### Full Example Code
+
+```solidity
+    function nativeTokenID(uint32 _foundrySN) public view returns (bytes memory) {
+        ERC20NativeTokens token = ERC20NativeTokens(
+            ISC.sandbox.erc20NativeTokensAddress(_foundrySN)
+        );
+        NativeTokenID memory id =token.nativeTokenID();
+        return id.data;
+    }
+```