update install_guide.md.

user_variables_by_threa

install_guide.md

@@ -151,12 +151,17 @@ MySQL 5.5 和 MySQL 8.0配置MySQL连接权限的 **_方式不一样_** ，分
 ### 数据库user_variables_by_thread报错
 
 - 错误现象
-SELECT command denied to user ‘root‘@‘192.168.*.*‘ for table ‘user_variables_by_thread‘报错
-普通mysql用户nature对performance_schema数据库的user_variables_by_thread表没有select权限
+
+  SELECT command denied to user ‘root‘@‘192.168.*.*‘ for table ‘user_variables_by_thread‘报错
+
+  普通mysql用户nature对performance_schema数据库的user_variables_by_thread表没有select权限
 
 - 解决方案
+
   登录mysql中root用户
+
   mysql> grant select on `performance_schema`.user_variables_by_thread to nature@"%";
+
   mysql> flush privileges;