feat: Added a privilege check example to Cookbook

Author: novusnota

pages/book/cookbook.mdx

@@ -535,4 +535,40 @@ let itemAddress: Address = contractAddress(self.getNftItemInit(itemIndex));
   [Tact collection and item contracts example](https://github.com/howardpen9/nft-template-in-tact/blob/tutorial/sources/contract.tact)\
   [FunC collection and item contracts example](https://github.com/Cosmodude/TAP/tree/main/contracts)
 
-</Callout>
+</Callout>
+
+## Receiving messages
+
+### How to check sender privileges using Ownable trait
+
+```tact
+// Ownable has to be imported from stdlib, as well as Deployable, for convenience:
+import "@stdlib/ownable";
+import "@stdlib/deploy";
+
+message FooBarMsg {
+    newVal: Int as uint32;
+}
+
+// Ownable trait can limit certain actions to the owner only
+contract SenderChecker with Deployable, Ownable {
+    owner: Address;     // Ownable trait requires you to add this exact state variable
+    val: Int as uint32; // some value
+
+    init() {
+        // we can initialize owner to any value we want, the deployer in this case:
+        self.owner = sender();
+        self.val = 0;
+    }
+
+    receive("inc") {
+        require(self.owner == sender(), "Only the owner can increase the value!");
+        self.val += 1;
+    }
+
+    receive(msg: FooBarMsg) {
+        require(self.owner == sender(), "Only the owner can set the value!");
+        self.val = msg.newVal;
+    }
+}
+```

pages/book/receive.mdx

@@ -4,20 +4,17 @@ TON is a distributed blockchain which means that communication between contracts
 
 ## Receive internal messages
 
-To receive a message of the required type, you need to declare a receiver function, for example, `receive("increment")`. This notation means the declaration of a `receiver` function that will be called when a text with the value `"increment"` is sent to the contract. The function body can modify the state of the contract and send messages to other contracts. It is impossible to call `receiver` directly. If you need to reuse some logic you can declare a function and call it from `receiver`.
+To receive a message of the required type, you need to declare a receiver function, for example, `receive("increment"){:tact}`. This notation means the declaration of a receiver function that will be called when a text with the value `"increment"{:tact}` is sent to the contract. The function body can modify the state of the contract and send messages to other contracts. It is impossible to call a receiver directly. If you need to reuse some logic you can declare a function and call it from the receiver.
 
 There are several receiver functions. All receiver functions are processed in the order they are listed below:
-* `receive()` - called when an empty message is sent to the contract
-* `receive("message")` - called when a text message with a specific comment is sent to the contract
-* `receive(str: String)` - called when an arbitrary text message is sent to the contract
-* `receive(msg: MyMessage)` - called when a binary message of type `MyMessage` is sent to the contract
-* `receive(msg: Slice)` - called when binary message of unknown type is sent to the contract
 
-
-## Example
+* `receive(){:tact}` - called when an empty message is sent to the contract
+* `receive("message"){:tact}` - called when a text message with a specific comment is sent to the contract
+* `receive(str: String){:tact}` - called when an arbitrary text message is sent to the contract
+* `receive(msg: MyMessage){:tact}` - called when a binary message of type `MyMessage` is sent to the contract
+* `receive(msg: Slice){:tact}` - called when binary message of unknown type is sent to the contract
 
 ```tact
-
 message MyMessage {
     value: Int;
 }