feat(js-client): Add OP Chain support

src/docs/sdk/js-client.md

@@ -1,20 +1,23 @@
 ---
-title: The OP Mainnet Client SDK
+title: The OP Stack Client SDK
 lang: en-US
 ---
 
 There are a few areas in which the SDK can help you navigate [the differences between OP Mainnet and Ethereum](../developers/build/differences/):
 
-
 - [Gas costs](../developers/build/transaction-fees.md)
 - [Interlayer communication](../developers/bridge/basics.md)
 
-## JavaScript SDK
+The SDK supports multiple OP Chains: OP, Base, Zora, etc.
+To see whether a specific OP Chain is supported directly, [see the documentation](https://sdk.optimism.io/enums/l2chainid).
+Chains that aren't officially supported just take a few extra steps.
+Get the L1 contract addresses, and [provide them to the SDK](https://stack.optimism.io/docs/build/sdk/#contract-addresses).
+Once you do that, you can use the SDK normally.
 
 [Reference](https://sdk.optimism.io/)
 
-Tutorials:
+## Tutorials:
 - [Viewing transactions between layers](https://github.com/ethereum-optimism/optimism-tutorial/tree/main/sdk-view-tx)
 - [Bridging ETH](https://github.com/ethereum-optimism/optimism-tutorial/tree/main/cross-dom-bridge-eth)
 - [Bridging ERC-20](https://github.com/ethereum-optimism/optimism-tutorial/tree/main/cross-dom-bridge-erc20)
-- [Estimate the costs of an Optimistic (L2) transaction](https://github.com/ethereum-optimism/optimism-tutorial/tree/main/sdk-estimate-gas)
+- [Estimate the costs of an Optimistic (L2) transaction](https://github.com/ethereum-optimism/optimism-tutorial/tree/main/sdk-estimate-gas)