Add vector to primitive types (#9)

Co-authored-by: aaron <[email protected]>

_pages/typecheck.md

@@ -48,7 +48,7 @@ local b2: B = a1 -- not ok
 
 ## Builtin types
 
-The Luau VM supports 9 primitive types: `nil`, `string`, `number`, `boolean`, `table`, `function`, `thread`, `userdata`, and `buffer`. Of these, `table` and `function` are not represented by name, but have their dedicated syntax as covered in this [syntax document](syntax), and `userdata` is represented by [concrete types](#roblox-types); other types can be specified by their name.
+The Luau VM supports 10 primitive types: `nil`, `string`, `number`, `boolean`, `table`, `function`, `thread`, `userdata`, `vector`, and `buffer`. Of these, `table` and `function` are not represented by name, but have their dedicated syntax as covered in this [syntax document](syntax), `userdata` is represented by [concrete types](#roblox-types), while `vector` is not representable by name at all; other types can be specified by their name.
 
 The type checker also provides the builtin types [`unknown`](#unknown-type), [`never`](#never-type), and [`any`](#any-type).