refactor: Update README to rename 'Customization' section to 'Usage Guides' and add 'Mapping Methods' link

(cherry picked from commit 7addd6e)

Author: arika0093

README.md

@@ -238,10 +238,11 @@ For more usage patterns and examples, see the [Usage Patterns Guide](./docs/libr
 * **[Installation](./docs/library/installation.md)** - Prerequisites, installation, and setup
 * **[Usage Patterns](./docs/library/usage-patterns.md)** - Anonymous, Explicit DTO, and Pre-existing DTO patterns
 
-### Customization
+### Usage Guides
 
 * **[Local Variable Capture](./docs/library/local-variable-capture.md)** - Using local variables in SelectExpr
 * **[Nested SelectExpr](./docs/library/nested-selectexpr.md) (beta)** - Using nested SelectExpr for reusable DTOs
+* **[Mapping Methods](./docs/library/mapping-methods.md)** - Generating mapping methods to class instead of interceptors
 * **[Array Nullability Removal](./docs/library/array-nullability.md)** - Automatic null handling for collections
 * **[Partial Classes](./docs/library/partial-classes.md)** - Extending generated DTOs
 * **[Nested DTO Naming](./docs/library/nested-dto-naming.md)** - Customizing nested DTO names