updated readme

cgattach.cpp

@@ -6,12 +6,12 @@ void print_usage() { fprintf(stdout, "usage: cgattach <pid> <cgroup>\n"); }
 int main(int argc, char *argv[]) {
   int flag=setuid(0);
   if (flag!=0) {
-    perror("cgattach setuid");
+    perror("cgattach need root");
     exit(EXIT_FAILURE);
   }
 
   if (argc != 3) {
-    error("only need 2 paramaters");
+    error("need exact 2 paramaters");
     print_usage();
     exit(EXIT_FAILURE);
   }