add cpp api reference (#618)

Summary: Pull Request resolved: #618

Differential Revision: D49924199

Author: JacobSzwejbka

.ci/docker/requirements-ci.txt

@@ -17,6 +17,8 @@ parameterized==0.9.0
 # Doc build requirements
 sphinx==5.0.0
 sphinx-gallery
+breathe==4.35.0
+exhale==0.3.6
 matplotlib
 # PyTorch Theme
 -e git+https://github.com/pytorch/pytorch_sphinx_theme.git#egg=pytorch_sphinx_theme