Add Viem documentation

Author: aefhm

clients/js/README.md

@@ -68,6 +68,19 @@ const provider = sapphire.wrap(window.ethereum);
 window.ethereum = sapphire.wrap(window.ethereum); // If you're feeling bold.
 ```
 
+### Viem
+
+```ts
+import { sapphireTestnet } from 'viem/chains';
+import * as sapphire from '@oasisprotocol/sapphire-paratime';
+
+const provider = sapphire.wrap(window.ethereum! as EIP1193Provider);
+const walletClient = createWalletClient({
+  chain: sapphireTestnet,
+  transport: custom(provider),
+});
+```
+
 ## Troubleshooting
 
 ### `Error: missing provider (operation="getChainId", code=UNSUPPORTED_OPERATION, ...)`

docs/guide.mdx

@@ -125,6 +125,25 @@ can also use those with Sapphire; all you need to do is set your Web3 gateway UR
 You can find the details of the Oasis Sapphire Web3 gateway
 [here](/dapp/sapphire#web3-gateway).
 
+#### Viem
+
+Sapphire will mostly work with Viem out of the box. You will need to import
+the Sapphire client, define the `chain`, and wrap your `provider` before
+creating a [custom] transport.
+
+[custom]: https://viem.sh/docs/clients/transports/custom.html
+
+```ts
+import { sapphireTestnet } from 'viem/chains';
+import * as sapphire from '@oasisprotocol/sapphire-paratime';
+
+const provider = sapphire.wrap(window.ethereum! as EIP1193Provider);
+const walletClient = createWalletClient({
+  chain: sapphireTestnet,
+  transport: custom(provider),
+});
+```
+
 ### Transactions & Calls
 
 <!-- https://github.com/oasisprotocol/docs/blob/455980674563cad92ff1e1b62a7a5f2d4d6809f0/docs/general/images/architecture/client-km-compute.svg -->