bpo-41661: Document os.path.relpath() exception on Windows with different drives (GH-25346)
diff --git a/Doc/library/os.path.rst b/Doc/library/os.path.rst
index e2f335e..4cab311 100644
--- a/Doc/library/os.path.rst
+++ b/Doc/library/os.path.rst
@@ -366,7 +366,8 @@
Return a relative filepath to *path* either from the current directory or
from an optional *start* directory. This is a path computation: the
filesystem is not accessed to confirm the existence or nature of *path* or
- *start*.
+ *start*. On Windows, :exc:`ValueError` is raised when *path* and *start*
+ are on different drives.
*start* defaults to :attr:`os.curdir`.