Add topics in pubspec.yaml (#567)

pubspec.yaml

diff --git a/pubspec.yaml b/pubspec.yaml
index fa5c897..76adf99 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -7,6 +7,11 @@
 description: Generator for FFI bindings, using LibClang to parse C header files.
 repository: https://github.com/dart-lang/ffigen
 
+topics:
+ - interop
+ - ffi
+ - codegen
+
 environment:
   sdk: ">=3.0.0-417.0.dev <4.0.0"