opl: added quickstart & monitoring link

docs/dapp/opl/README.md

@@ -10,11 +10,60 @@ The Oasis Privacy Layer contains a set of [smart contracts](https://github.com/o
 that integrate [Sapphire](../sapphire/README.mdx) into your existing and future
 Web3 applications and introduce confidentiality.
 
-Application developers on any EVM-compatible network can add confidential state
+Application developers on [any supported network](https://im-docs.celer.network/developer/contract-addresses-and-rpc-info) can add confidential state
 and selective disclosures to their applications through the usage of a smart
 contract deployed on OPL without leaving their existing networks.
 
 For more information about OPL and to catch the latest news, please visit the
 official [page](https://oasisprotocol.org/opl).
 
 ![Oasis Privacy Layer diagram](../images/opl/privacy-layer-diagram.png)
+
+## Quickstart
+
+A pair of contracts are linked bidirectionally to each other across chains, with one end on Sapphire and the other on a supported EVM compatible chain (the Home Network). They can post and receive messages to & from each other using the message-passing bridge, but must register endpoints to define which messages they handle.
+
+Start by adding the `sapphire-contracts` package to your project so you can import `OPL.sol`:
+
+    pnpm add @oasisprotocol/sapphire-contracts
+
+Then define the two contracts, starting with a contract on Sapphire which runs inside the confidential enclave and can be called via the `secretExample` handler. It is provided with the address of the other contract and the network it exists on via the constructor:
+
+```solidity
+import {Enclave, Result, autoswitch} from "@oasisprotocol/sapphire-contracts/contracts/OPL.sol";
+
+contract SapphireContract is Enclave {
+    constructor(address otherEnd, string chain) Enclave(otherEnd, autoswitch(chain)) {
+        registerEndpoint("secretExample", on_example);
+    }
+    function on_example(bytes calldata _args) internal returns (Result) {
+        (uint256 a, bool b) = abi.decode(args, (uint256, bool));
+        // TODO: do confidential things here
+        return Result.Success;
+    }
+}
+```
+
+Then on the other chain, define your contract which can be called via `triggerExample` to send a message to the contract on Sapphire using the `postMessage` interface.
+
+```solidity
+import {Host, Result} from "@oasisprotocol/sapphire-contracts/contracts/OPL.sol";
+
+contract HomeContract is Host {
+    constructor(address otherEnd) Host(otherEnd) {
+    }
+    function triggerExample (uint256 a, bool b) external payable {
+        postMessage("secretExample", abi.encode(a, b));
+    }
+}
+```
+
+After a few minutes the bridge will detect and then execute the `SapphireContract.on_example` method.
+
+## Monitoring
+
+The Celer IM Scan API can be used to retrieve status and message details by providing the globally unique transaction ID from the chain which originated the message.
+
+    https://api.celerscan.com/scan/searchByTxHash?tx=0x...
+
+For details of the response format, see the [Query IM Tx Status](https://im-docs.celer.network/developer/development-guide/query-im-tx-status) page of the Celer Inter-Chain Message (IM) documentation.