feat: polygon hook doc

docs/reference/hooks/polygon-pos.mdx

@@ -0,0 +1,47 @@
+# Polygon PoS Hook
+
+Polygon PoS has their own interface for message passing between Ethereum and Polygon called the [`fx portal`](https://github.com/0xPolygon/fx-portal). Messages passed via this interface benefit from the security of the Polygon [state sync mechanism](https://docs.polygon.technology/pos/architecture/bor/state-sync/).
+
+To provide this security as an option in Hyperlane, we created a Hook and ISM combo that can be transparently configured to reuse the fx-portal interface.
+
+See the [addresses](../contract-addresses.mdx) page for Hook and ISM addresses. 
+
+## How It Works
+
+Polygon FX-Portal provide FxChild (FxChild.sol) and FxRoot (FxRoot.sol) as the main contracts on which the bridge works. It calls and passes data to user-defined methods on another chain without needing a mapping.
+
+The FxChild/FxRoot contract are provided and maintained by the polygon team. You can find the address of this contract in Polygon’s [Fx-Portal repo](https://github.com/0xPolygon/fx-portal). 
+The PolygonPosHook sends payloads with FxRoot. Validators will pick up the message and pass it to the other chain. You can find detailed state sync mechanism in [documentation](https://docs.polygon.technology/pos/how-to/bridging/l1-l2-communication/state-transfer/) `StateReceiver` at `0x0000000000000000000000000000000000001001` is allowed to call `onStateReceive` in FxChild contract. FxChild calls `processMessageFromRoot` in abstract `CrossChainEnabledPolygonChild` on which PolygonPosISM implements. `CrossChainEnabledPolygonChild` is maintained by [OpenZeppelin](https://docs.openzeppelin.com/contracts/4.x/api/crosschain#) 
+
+```mermaid
+flowchart TB
+    subgraph Origin Ethereum
+      Sender
+      M_O[(Mailbox)]
+      Hook[PolygonPosHook]
+      Eth[(FxRoot)]
+
+      Sender -- "dispatch(...)" --> M_O
+      M_O -- "postDispatch(message)" --> Hook
+      Hook -- "sendMessage(messageId)" --> Eth
+    end
+
+    M_O -. "relay" .-> M_D
+    Eth -. "validator node" .-> Polygon
+
+    subgraph Destination Polygon PoS
+      Recipient
+      M_D[(Mailbox)]
+      ISM{PolygonPosISM}
+      Polygon[(FxChild)]
+
+      M_D -- "verify(..., message)" --> ISM
+      M_D -- "handle(...)" --> Recipient
+      ISM -. "interchainSecurityModule()" .- Recipient
+
+      Polygon -- "verifyMessageId(messageId)" --> ISM
+    end
+
+    style Eth fill: #ff0402
+    style Polygon fill: #ff0402
+```

sidebars.js

@@ -86,6 +86,11 @@ const sidebars = {
           id: "reference/hooks/op-stack",
           label: "OP Stack",
         },
+        {
+          type: "doc",
+          id: "reference/hooks/polygon-pos",
+          label: "Polygon PoS",
+        },
       ],
     },
     {