dev/release/README.md is outdated

[iajoiner]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
(This section helps Arrow developers understand the context and why for this feature, in addition to the what)
The dev/release/README.md is already outdated since Ballista is its own repo now and that DataFusion has 2 releases per month.
Describe the solution you'd like
A clear and concise description of what you want to happen.
Edit dev/release/README.md so that it is more up to date.
Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.
We can make the changes while releasing Ballista 0.8.0 which I can help with.

[andygrove]

Hi @iajoiner - please see #183