docs: Document duplicate license message behavior and fixes

docs/source/License-configuration.md

@@ -30,6 +30,47 @@ There is no other license enforcement besides log messages. No central license s
 
 The log messages are logged using standard `Microsoft.Extensions.Logging` loggers under the category name `LuckyPennySoftware.AutoMapper.License`.
 
+### Multiple License Messages
+
+If you see duplicate license log messages at startup, this is typically caused by AutoMapper being registered or configured more than once in your application.
+
+#### Using `AddAutoMapper` (Microsoft.Extensions.DependencyInjection)
+
+Calling `AddAutoMapper` multiple times in the same `IServiceCollection` is safe. After the first call registers `IMapper`, subsequent calls are ignored and no additional license validation occurs:
+
+```c#
+services.AddAutoMapper(cfg => { cfg.LicenseKey = "key"; });
+services.AddAutoMapper(cfg => { /* ignored -- IMapper already registered */ });
+```
+
+If you are calling `AddAutoMapper` in multiple places (e.g. in modular startup code), each call still only results in a single `MapperConfiguration` singleton and a single license log message.
+
+#### Using `MapperConfiguration` Directly
+
+When creating `MapperConfiguration` instances manually, each instance performs its own license validation, producing a separate log message:
+
+```c#
+// Each of these logs a license message – avoid creating multiple instances
+var config1 = new MapperConfiguration(cfg => { cfg.LicenseKey = "key"; }, loggerFactory);
+var config2 = new MapperConfiguration(cfg => { cfg.LicenseKey = "key"; }, loggerFactory);
+```
+
+To avoid duplicate messages, create and reuse a single `MapperConfiguration` instance for the lifetime of your application, typically registered as a singleton:
+
+```c#
+// Create once and reuse
+var config = new MapperConfiguration(cfg => { cfg.LicenseKey = "key"; }, loggerFactory);
+var mapper = new Mapper(config);
+```
+
+#### Suppressing Duplicate License Messages
+
+If you intentionally have multiple configurations (for example in integration tests or modular scenarios), you can silence duplicate license log messages by filtering the log category:
+
+```csharp
+builder.Logging.AddFilter("LuckyPennySoftware.AutoMapper.License", LogLevel.None);
+```
+
 ### Client Redistribution Scenarios
 
 In the case where AutoMapper is used on a client, including: