Update readme for Unity

README.md

@@ -234,6 +234,8 @@ dotnet add package MagicOnion
     - [Support for Unity client](#support-for-unity-client)
         - [iOS build with gRPC](#ios-build-with-grpc)
         - [Stripping debug symbols from ios/libgrpc.a](#stripping-debug-symbols-from-ioslibgrpca)
+        - [Stripping debug symbols from libgrpc_csharp_ext.so](#stripping-debug-symbols-from-libgrpccsharpextso)
+        - [Workaround for il2cpp + Windows Build failure](#workaround-for-il2cpp--windows-build-failure)
     - [gRPC Keepalive](#grpc-keepalive)
 - [HTTPS (TLS)](#https-tls)
 - [Deployment](#deployment)
@@ -1163,6 +1165,44 @@ $ rm libgrpc.a && mv libgrpc_stripped.a libgrpc.a
 
 Make sure you can build app with iOS and works fine.
 
+## Stripping debug symbols from libgrpc_csharp_ext.so
+Plugins/Grpc.Core/runtime/android/[arch]/libgrpc_csharp_ext.so file size is big because its includes debug symbols.
+
+You can reduce its size using strip (this command is includes in the NDK).
+
+```shell
+$ cd ${UNITY_PATH}/Plugins/Grpc.Core/runtime/android/${TARGET_ARCH}
+$ strip.exe libgrpc_csharp_ext.so
+```
+
+## Workaround for il2cpp + Windows Build failure
+If you do a Windows il2cpp build with the gRPC daily build, the build may fail with following error messages.
+
+```
+20AAB1A42EE7F9CA535031CD347327DE.obj : error LNK2019: unresolved external symbol dlopen referenced in function Mono_dlopen_m7F2DE2CD0870AB15EEA4E0A0BA6C47044E74BB67
+20AAB1A42EE7F9CA535031CD347327DE.obj : error LNK2019: unresolved external symbol dlerror referenced in function Mono_dlerror_m359ABCFD23D0EB5314DE2DFF8AB58CFE949BBABD
+20AAB1A42EE7F9CA535031CD347327DE.obj : error LNK2019: unresolved external symbol dlsym referenced in function Mono_dlsym_m31A00C09F598C9D552A94628C2C28B3C7B04C2DD
+C:\Path\To\MyProject\Library\il2cpp_cache\linkresult_C1E926E002526A4D380E4B12B6BD0522\GameAssembly.dll : fatal error LNK1120: 3 unresolved externals
+```
+
+The reason is because some native function (but not nessessary at the runtime) not found on Windows il2cpp build.
+You can avoid this problem by adding the following code to `grpc_csharp_ext_dummy_stubs.c`.
+
+```c
+void* dlopen(const char* filename, int flags) {
+  fprintf(stderr, "Should never reach here");
+  abort();
+}
+char* dlerror(void) {
+  fprintf(stderr, "Should never reach here");
+  abort();
+}
+void* dlsym(void* handle, const char* symbol) {
+  fprintf(stderr, "Should never reach here");
+  abort();
+}
+```
+
 ## gRPC Keepalive
 When you want detect network termination on Client or vice-versa, you can configure gRPC Keepalive.