deploying.md

To deploy to opam

• update /tablecloth-base.opam to version x.y.z
• git tag -f x.y.z
• git push origin x.y.z
• opam-publish tablecloth-base -v x.y.z https://github.com/darklang/tablecloth/archive/x.y.z.tar.gz
• make the pull request work