fix doc build (#1087)

Co-authored-by: Min Xu <min.xu.public@gmail.com>

docs/requirements.txt

@@ -3,4 +3,6 @@ sphinx==4.2.0
 sphinx_rtd_theme==0.4.3
 sphinxcontrib-programoutput==0.16
 git+https://github.com/pytorch/pytorch_sphinx_theme.git#egg=pytorch_sphinx_theme
+# Need to sync with fairscale's requirements.txt below
 torch>=1.6.0
+numpy >= 1.22.0

requirements.txt

 # FairScale should only depends on torch, not things higher level than torch.
-# Note1: setup.py automatically reads this file to setup install time dependencies.
+# Note1: setup.py automatically reads this file to setup install-time dependencies.
 # Note2: we use >= in this file but == in requirements-dev.txt for determinism
 #        in testing.
+# Note3: update docs/requirements.txt if you change this file.
 torch >= 1.8.0
 numpy >= 1.22.0