[3.9] bpo-41082: Add note on errors that may be raised by home() and expanduser() (GH-28186)

Co-authored-by: Łukasz Langa <[email protected]>

Author: akulakov

Doc/library/pathlib.rst

@@ -708,6 +708,10 @@ call fails (for example because the path doesn't exist).
       >>> Path.home()
       PosixPath('/home/antoine')
 
+   Note that unlike :func:`os.path.expanduser`, on POSIX systems a
+   :exc:`KeyError` or :exc:`RuntimeError` will be raised, and on Windows systems a
+   :exc:`RuntimeError` will be raised if home directory can't be resolved.
+
    .. versionadded:: 3.5
 
 
@@ -764,6 +768,10 @@ call fails (for example because the path doesn't exist).
       >>> p.expanduser()
       PosixPath('/home/eric/films/Monty Python')
 
+   Note that unlike :func:`os.path.expanduser`, on POSIX systems a
+   :exc:`KeyError` or :exc:`RuntimeError` will be raised, and on Windows systems a
+   :exc:`RuntimeError` will be raised if home directory can't be resolved.
+
    .. versionadded:: 3.5