Add AccessManager guide (#4691)

Co-authored-by: Hadrien Croubois <hadrien.croubois@gmail.com>
Co-authored-by: Eric Lau <ericglau@outlook.com>
Co-authored-by: Zack Reneau-Wedeen <z.reneau.wedeen@gmail.com>

contracts/mocks/docs/access-control/MyContractOwnable.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.20;
+
+import {Ownable} from "../../../access/Ownable.sol";
+
+contract MyContract is Ownable {
+    constructor(address initialOwner) Ownable(initialOwner) {}
+
+    function normalThing() public {
+        // anyone can call this normalThing()
+    }
+
+    function specialThing() public onlyOwner {
+        // only the owner can call specialThing()!
+    }
+}