Various improvements.

README.md

@@ -75,6 +75,30 @@ func main() {
 - `serial.RandomCode(isInUse ...func(uint32) bool) (string, uint32, error)`
 	- Generates a random valid `LLL-NNN-LC` code and its corresponding index.
 	- If provided, the callback is used to skip indices already in use by the client.
+- `serial.RandomCodeWithOptions(options serial.RandomCodeOptions) (string, uint32, error)`
+	- Configurable variant with `MaxAttempts`, `IsInUse`, and custom `RandomIndex` source.
+
+Example with options:
+
+```go
+// See the runnable command at ./cmd/triplex-example/main.go
+```
+
+## Commands
+
+Runnable example command:
+
+```bash
+go run ./cmd/triplex-example
+```
+
+Using Makefile:
+
+```bash
+make run-example
+make build-example
+make test
+```
 
 Exported errors:
 
@@ -85,7 +109,8 @@ Exported errors:
 - `serial.ErrNumberOutOfRange`
 - `serial.ErrInvalidChecksum`
 - `serial.ErrIndexOutOfRange`
-- `serial.ErrRandomGenerationFailed`
+- `serial.ErrRandomSourceFailed`
+- `serial.ErrNoAvailableIndex`
 
 ## Testing