[ORC] Start adding ORCv1 to ORCv2 transition tips to the ORCv2 doc.
Hi Lang, I am getting these warnings from ninja docs-llvm-html:
llvm/docs/ORCv2.rst:614: WARNING: Footnote  is not referenced. llvm/docs/ORCv2.rst:623: WARNING: Footnote  is not referenced. llvm/docs/ORCv2.rst:629: WARNING: Footnote  is not referenced.
The default invocation treats warnings as errors, this basically breaks the build. It's not the only places, but yours show up first.