fix README

README.md

@@ -17,14 +17,14 @@ IaaS software have been suffered for a long time.
 In terms of complexity, ZStack sticks to the design principles of APIs managing everything, full automation, self-managed services,
 no hardware lockin, and user-friendly query APIs, providing a software easy to setup and long-term operation.
 
-In terms of stability, ZStack was born with a plugin system that adding or removing features will not impact existing code,
+In terms of stability, ZStack was born with a plugin system that adding or removing features will not impact existing codes,
 a workflow engine that can rollback completed changes on error, a cascade framework that can spread an operation from
 a resource to dependent resources, and three rigorous automated testing systems that guard every single feature,
 solving the stability issue in architectural designs.
 
-Besides, ZStack is extremely scale that a single management node is capable of managing hundreds of thousands of
+Besides, ZStack is extremely scalable that a single management node is capable of managing hundreds of thousands of
 physical servers, managing millions of virtual machines, and serving tens of thousands of concurrent API requests,
-particular suitable for building large, scalable public clouds.
+particular suitable for building large-scale public clouds.
 
 
 ## Installation