Build dev doc
This should be nearly good to go, only need to check that on close it doesn't actually regenerate the modifications of the PR.

Will take a stab at that tomorrow morning cc @sgugger @mishig25 <|||||>Will only need to change the target of the `git add` directive and it should be good to go<|||||>As said in private, this won't work for branches that have a different origin than `transformers`, since those won't get access to the secrets for security reasons.