docs: update r8-proguard

Author: fankes

docs-source/src/en/config/r8-proguard.md

@@ -7,6 +7,9 @@ If you are using the [kavaref-extension](../library/kavaref-extension) module an
 
 ```
 -keepattributes Signature
+-keep class * extends com.highcapable.kavaref.extension.TypeRef {
+    <init>(...);
+}
 ```
 
 `TypeRef` has been annotated with `Keep`. If it doesn't work, please manually add the following rules to keep the class.

docs-source/src/zh-cn/config/r8-proguard.md

@@ -6,6 +6,9 @@
 
 ```
 -keepattributes Signature
+-keep class * extends com.highcapable.kavaref.extension.TypeRef {
+    <init>(...);
+}
 ```
 
 `TypeRef` 已添加 `Keep` 注解，如果无效，请手动添加以下规则以保留类。