Update README.md (facebookresearch#446)

Fixed typo in README.md hyperlink to docs directory

README.md

@@ -49,7 +49,7 @@ width="800px"></p>
 See the [release notes](./docs/release.md) for more details.
 
 - 22/02/2023: added support for the [SDX 2023 Challenge](https://www.aicrowd.com/challenges/sound-demixing-challenge-2023),
-    see the dedicated [doc page](./doc/sdx23.md)
+    see the dedicated [doc page](./docs/sdx23.md)
 - 07/12/2022: Demucs v4 now on PyPI. **htdemucs** model now used by default. Also releasing
     a 6 sources models (adding `guitar` and `piano`, although the latter doesn't work so well at the moment).
 - 16/11/2022: Added the new **Hybrid Transformer Demucs v4** models.