Add Viem documentation

Author: aefhm

clients/js/README.md

@@ -68,6 +68,44 @@ const provider = sapphire.wrap(window.ethereum);
 window.ethereum = sapphire.wrap(window.ethereum); // If you're feeling bold.
 ```
 
+### Viem
+
+```ts
+import * as sapphire from '@oasisprotocol/sapphire-paratime';
+
+const sapphireChainTestnet: Chain = {
+  id: sapphire.NETWORKS.testnet.chainId,
+  name: 'Sapphire',
+  network: 'sapphire',
+  nativeCurrency: {
+    decimals: 18,
+    name: 'Sapphire',
+    symbol: 'ROSE',
+  },
+  rpcUrls: {
+    default: {
+      http: [sapphire.NETWORKS.testnet.defaultGateway],
+    },
+    public: {
+      http: [sapphire.NETWORKS.testnet.defaultGateway],
+    },
+  },
+  blockExplorers: {
+    default: {
+      name: 'Sapphire Explorer (Testnet)',
+      url: sapphire.NETWORKS.testnet.defaultGateway,
+    },
+  },
+  testnet: true,
+};
+
+const provider = sapphire.wrap(window.ethereum! as EIP1193Provider);
+const walletClient = createWalletClient({
+  chain: sapphireChainTestnet,
+  transport: custom(provider),
+});
+```
+
 ## Troubleshooting
 
 ### `Error: missing provider (operation="getChainId", code=UNSUPPORTED_OPERATION, ...)`