Add go-kit example proto definitions

examples/go-kit/services/session/session.proto

@@ -0,0 +1,26 @@
+syntax "proto3";
+
+package session;
+
+service SessionService {
+  rpc Login(LoginRequest) returns (LoginResponse) {}
+  rpc Logout(LogoutRequest) returns (LogoutResponse) {}
+}
+
+message LoginRequest {
+  string username = 1;
+  string password = 2;
+}
+
+message LoginResponse {
+  string token = 1;
+  string err_msg = 2;
+}
+
+message LogoutRequest {
+  string token = 1;
+}
+
+message LogoutResponse {
+  string err_msg = 1;
+}