update docs

Author: tqchen

.github/workflows/publish_tvm_ffi_docs.yml

@@ -22,6 +22,10 @@ jobs:
           submodules: recursive
           path: tvm
 
+      - name: Install doxygen
+        run: |
+          sudo apt install -y doxygen graphviz
+
       - name: Install wheel and requirements
         working-directory: tvm/ffi
         run: |
@@ -31,6 +35,8 @@ jobs:
 
       - name: Build docs
         working-directory: tvm/ffi/docs
+        env:
+          BUILD_CPP_DOCS: 1
         run: |
           make html
           python ../../../tvm-site/scripts/download_3rdparty_embeds.py -v --path=_build/html