Fix link to documentation in README (#3184)

As the title describes, it should be that [this
PR](#3078) did not
synchronize the modification of the root directory's README.

Co-authored-by: zhaohaiyuan <[email protected]>

Author: zhaohaidao

README.md

@@ -39,7 +39,7 @@ layer on which more complex systems can be constructed.
 
 ## Documentation
 
-* [Documentation Home](docs/index.md)
+* [Documentation Home](docs/sphinx/source/index.md)
 * [Contributing](CONTRIBUTING.md)
 * [Code of Conduct](CODE_OF_CONDUCT.md)
 * [License](LICENSE)