Update README.md

Fixed grammatical errors

README.md

@@ -7,8 +7,8 @@ implementation and native code generation facility using LLVM toolchain.
 
  _Kotlin/Native_ is primarily designed to allow compilation for platforms where
 virtual machines are not desirable or possible (such as iOS, embedded targets),
-or where developer is willing to produce reasonably-sized self-contained program
-without need to ship an additional execution runtime.
+or where a developer is willing to produce a reasonably-sized self-contained program
+without the need to ship an additional execution runtime.
 
 To compile from sources use following steps.