modify readme

Former-commit-id: d5fe9fbbe444e2580714ad4fc741b61048dbe01c

cpp/README.md

@@ -2,10 +2,10 @@
 #### Step 1: install necessery tools
 
     centos7 : 
-        yum install gfortran libsqlite3-dev libsnappy-dev zlib bzip2
+        yum install gfortran libsqlite3-dev libsnappy-dev libzstd-dev bzip2
         
     ubuntu16.04 : 
-        sudo apt-get install gfortran libsqlite3-dev libsnappy-dev zstd bzip2
+        sudo apt-get install gfortran libsqlite3-dev libsnappy-dev libzstd-dev bzip2
 
 #### Step 2: build third-parties
 Note: If you want to debug into third-parties, you can build debug with CXXFLAGS='-g -O0' with option