update custom_components.md to use Kotlin and reflect current API (#…

…424)

* update `custom_components.md` to reflect current API

* add explanation about creating custom ImagePickerComponents

docs/custom_components.md

@@ -1,12 +1,23 @@
 # Custom Components
 
 You also can change how to process the image and how to get the image files through `ImageLoader` and `ImageFileLoader`
-To change this, simply set it on `ImagePickerComponentHolder`
+To change this, first, create custom `ImagePickerComponents`.
+You could inherit from `DefaultImagePickerComponents` or directly implements from `ImagePickerComponents` interface.
 
-```java
-ImagePickerComponentHolder.getInstance()
-	.setImageLoader(new GrayScaleImageLoader())
-	.setImageFileLoader(new WebpImageFileLoader())
-```	
+```kotlin
+class CustomImagePickerComponents(
+    context: Context
+) : DefaultImagePickerComponents(context.applicationContext) {
+    override val imageLoader: ImageLoader
+        get() = GrayscaleImageLoader()
+}
+```
 
-Happy coding!
+Then, use it by calling `setInternalComponent` on `ImagePickerComponentsHolder`.
+```kotlin
+ImagePickerComponentsHolder.setInternalComponent(
+    CustomImagePickerComponents(context)
+)
+```
+
+Happy coding!