Update documentation to match more aggressive absolute path exclusion in resources.

changelog.d/1635.change.rst

-Resource paths are passed to ``pkg_resources.resource_string`` and similar no longer accept paths that traverse parents or begin with a leading ``/``. Violations of this expectation raise DeprecationWarnings and will become errors.
+Resource paths are passed to ``pkg_resources.resource_string`` and similar no longer accept paths that traverse parents, that begin with a leading ``/``. Violations of this expectation raise DeprecationWarnings and will become errors. Additionally, any paths that are absolute on Windows are strictly disallowed and will raise ValueErrors.

docs/pkg_resources.txt

@@ -1133,8 +1133,7 @@ segment will be treated as a peer of the top-level modules or packages in the
 distribution.
 
 Note that resource names must be ``/``-separated paths rooted at the package,
-cannot contain relative names like ``".."``, and cannot begin with a
-leading ``/``.  Do *not* use
+cannot contain relative names like ``".."``, and cannot be absolute.  Do *not* use
 ``os.path`` routines to manipulate resource paths, as they are *not* filesystem
 paths.