Add explanations of the yield statement to common_issues.rst

Author: vortexie

docs/source/common_issues.rst

@@ -856,19 +856,19 @@ generator function (https://peps.python.org/pep-0255/#specification-yield).
 .. code-block:: python
 
     from collections.abc import Generator, AsyncGenerator
-    
+
     async def async_gen() -> AsyncGenerator[int]:
         yield 1
-    
+
     def gen() -> Generator[int]:
         yield 1
-    
+
     async def async_func() -> int:
         return 1
-    
+
     def func() -> int:
         return 1
-    
+
     reveal_type(async_gen())  # AsyncGenerator[int, None]
     reveal_type(gen())        # Generator[int, None, None]
     reveal_type(async_func()) # Coroutine[Any, Any, int]
@@ -881,13 +881,13 @@ of such functions as Generator (or AsyncGenerator when the function is async).
 
 A common mistake is that we declared the return type of a function as
 Generator (AsyncGenerator) but did not use the ``yield`` statement in the function.
-``mypy`` will consider that the return type (normal type) of this function
+``mypy`` will consider that the return type (no return, or normal types) of this function
 does not meet the expectation (generator type).
 
 .. code-block:: python
 
     from collections.abc import Generator
-    
+
     def gen() -> Generator[int]:
         ... # error: Missing return statement