[hack] move opam mini repo in its own subdir
[hack] move opam mini repo in its own subdir

Summary: This is just so that the README make more sense. I had to do that in a separate diff to avoid merge conflict on opam-mini-repo.tar.gz

Reviewed By: vassilmladenov

Differential Revision: D13027425

fbshipit-source-id: 700e1ded451628f70c870390847164c14c98d0bc

popham/flow,mroch/flow,gabelevi/flow,popham/flow,popham/flow,samwgoldman/flow,facebook/flow,facebook/flow,AgentME/flow,samwgoldman/flow,mroch/flow,facebook/flow,samwgoldman/flow,samwgoldman/flow,mroch/flow,samwgoldman/flow,gabelevi/flow,gabelevi/flow,popham/flow,samwgoldman/flow,gabelevi/flow,mroch/flow,popham/flow,facebook/flow,mroch/flow,mroch/flow,AgentME/flow,gabelevi/flow,AgentME/flow,facebook/flow,samwgoldman/flow,facebook/flow,popham/flow,mroch/flow,gabelevi/flow,AgentME/flow,facebook/flow,AgentME/flow,popham/flow,gabelevi/flow