Issue #28091: Document PEP 525 & PEP 530.

Patch by Eric Appelt.
(grafted from 78c8f450b84ca1864123ec487d363eb151f61a4a)
diff --git a/Doc/library/inspect.rst b/Doc/library/inspect.rst
index de0c301..41a784d 100644
--- a/Doc/library/inspect.rst
+++ b/Doc/library/inspect.rst
@@ -318,6 +318,27 @@
    .. versionadded:: 3.5
 
 
+.. function:: isasyncgenfunction(object)
+
+   Return true if the object is an :term:`asynchronous generator` function,
+   for example::
+
+    >>> async def agen():
+    ...     yield 1
+    ...
+    >>> inspect.isasyncgenfunction(agen)
+    True
+
+   .. versionadded:: 3.6
+
+
+.. function:: isasyncgen(object)
+
+   Return true if the object is an :term:`asynchronous generator iterator`
+   created by an :term:`asynchronous generator` function.
+
+   .. versionadded:: 3.6
+
 .. function:: istraceback(object)
 
    Return true if the object is a traceback.