[fix]: experimental import fix (#1043)

* [fix]: experimental import fix

* Update fairscale/experimental/__init__.py

* Update fairscale/experimental/__init__.py
Co-authored-by: Min Xu <min.xu.public@gmail.com>

fairscale/experimental/__init__.py

@@ -9,6 +9,8 @@
 
 from typing import List
 
-from . import nn, optim, wgit
+# Don't import sub-modules as experimental stuff otherwise gets imported directly
+# when user does an `import fairscale`. This can cause experimental code's import
+# dependencies (like pygit2) to be leaked into the fairscale main code.
 
 __all__: List[str] = []