Update README.md for safe_mapping

packages/auto_mappr/README.md

@@ -41,6 +41,7 @@ Heavily inspired by [C# AutoMapper][auto_mapper_net_link].
   - [Mapping from source](#mapping-from-source)
   - [Nullability handling](#nullability-handling)
     - [Forced non-nullable field for nullable source](#forced-non-nullable-field-for-nullable-source)
+  - [Safe mapping](#safe-mapping)
   - [Generics](#generics)
   - [Library import aliases](#library-import-aliases)
   - [Modules](#modules)
@@ -479,7 +480,7 @@ This is by design and it is up to developer decide if bang operator is appropiat
   ```yaml
    $default:
     builders:
-      :auto_mappr:
+       auto_mappr:
         options:
           ignoreNullableSourceField: true
   ```
@@ -488,6 +489,37 @@ This is by design and it is up to developer decide if bang operator is appropiat
 
 Precedense is `global configuration` -> `MapType` -> `Field` -> defaults to false.
 
+### Safe mapping
+Sometimes it can happen that mapping goes wrong and exception is thrown. Typically it can be caused 
+by mapping from source with a nullable variable to a target with a corresponding non-nullable variable. 
+If you want to avoid propagating the exception through the app, auto_mappr can catch it and return null instead. In case you want to know
+that something went wrong during the mapping there is a `onMappingError` callback that is invoked each time error occurs. If you want enable
+safe mapping, it can be done either on the global level in `build.yaml` with `safeMapping` option
+
+  ```yaml
+   $default:
+    builders:
+      auto_mappr:
+        options:
+          safeMapping: true
+  ```
+
+or individually for each `MapType`:
+
+```dart
+@AutoMappr([
+  MapType<UserDto, User>(
+    safeMapping: true,
+  ),
+])
+class Mappr extends $Mappr {}
+```
+Note that global `safeMapping` has always the priority.
+
+Safe mapping can be done only through `tryConvert`, `tryConvertIterable`, `tryConvertList` or `tryConvertSet` methods. All of them have an optional parameter
+`void Function(Object error, StackTrace stackTrace, SOURCE? source)? onMappingError`, which is a callback function triggered whenever an exception occurs during the mapping process.
+This can be used fo example for logging the error.
+
 ### Generics
 
 AutoMappr can handle generics, so you can map objects with type arguments with ease.