Add section for events

chapters/smart-contracts/lab/content/events.md

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+# Events
+
+Key Takeaways:
+* Events in smart contracts serve as a communication mechanism between the contract and user interfaces;
+* By emitting events, smart contracts can notify external applications or listeners about specific actions or changes;
+* Events play a key role in facilitating effective interaction with user interfaces while ensuring secure automated execution of code-based agreements.
+
+## Example of events
+
+Notice the **Logs** section near the **Transaction Details**.
+![ESDTNFTCreate](../media/nft_create.png)
+
+This section shows all the events this transaction emitted.
+Notice that most transactions have this **Logs** section.
+
+![ESDTNFTTransfer](../media/nft_transfer.png)
+
+Let's open this tab and inspect the Events
+
+![ESDTNFTTransfer Event](../media/nft_transfer_event.png)
+
+Notice there are 4 data fields:
+* `SBPT-774fbd` - the token ID;
+* `1` - the nonce;
+* `1` - the value (the *Smart* display feature doesn't know how to interpret that but the *Decimal* option does);
+* `erd1ld6er5zpdze3cynzkapur9qhzh826jje6n87g7tvdfrtszs8jn2qv44nqd` - the destination address.
+
+
+Let's inspect a more complex operation and check all the log events.
+[Here](https://explorer.multiversx.com/transactions/4f85a8ca33fb5d7ca336d61e6014d96c57048ffb7ee2d9f290bb0a7c1c7c87ff) is the link to the transaction.
+
+![Swap Transaction](../media/swap_tx.png)
+
+Notice that the transaction has 4 transfers and 1 burn operations.
+Let's inspect the logs:
+
+![Swap Event1](../media/swap_logs1.png)
+
+The first transaction is an `ESDTTransfer` for the token `USDC-c76f1f` which has 6 decimals; therefore *580345261* is equal to *580,345261$*.
+You can match the events to the **Token Operations** from the Transacton Details.
+
+You can check the `deposit_swap_fees_event` code [here](https://github.com/multiversx/mx-exchange-sc/blob/e4b95afa68273bab34b4124b711f28af9677e029/energy-integration/fees-collector/src/events.rs#L16).
+
+Notice the burn event below. Keep in mind that `MEX-455c57` has 18 decimals.
+![Swap Event2](../media/swap_logs2.png)
+
+[Here](https://github.com/multiversx/mx-exchange-sc/blob/e4b95afa68273bab34b4124b711f28af9677e029/dex/pair/src/events.rs#L202) is the code for the `swap_no_fee_and_forward` event.
+
+## Writing your own event in the Smart Contract
+
+The structure of an event is:
+```rust
+    #[event("your_event_name")]
+    fn the_function_you_call_when_you_want_to_emit_en_event(
+        &self,
+        #[indexed] field1: &TokenIdentifier,
+        #[indexed] field2: &ManagedAddress,
+        #[indexed] field3: u64,
+        #[indexed] field4: BigUint,
+    );
+```
+
+And when you want to emit an event, just call the function:
+```rust
+    self.the_function_you_call_when_you_want_to_emit_en_event(field1, field2, field3, field4);
+```