[doc] Minor improvements to is_typeddict (GH-22280)



1. The check is on the type
2. Add link to TypeDict
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
index bfff81e..d31c65d 100644
--- a/Doc/library/typing.rst
+++ b/Doc/library/typing.rst
@@ -1660,7 +1660,7 @@
 
 .. function:: is_typeddict(tp)
 
-   Check if an annotation is a TypedDict class.
+   Check if a type is a :class:`TypedDict`.
 
    For example::
         class Film(TypedDict):