Improve grammar (#1805)

diff --git a/docs/builtin-classes.md b/docs/builtin-classes.md
index a03cc84..1327f8f 100644
--- a/docs/builtin-classes.md
+++ b/docs/builtin-classes.md
@@ -146,7 +146,7 @@
 as the following example shows.
 
 ```kotlin          
-// @Serializable annotation is not need for a enum classes
+// The @Serializable annotation is not needed for enum classes
 enum class Status { SUPPORTED }
         
 @Serializable