The instructions are posted here:
You have to install Oracle DB or client, then you can extract the fully managed provider files.
When ODAC 12c is released, we'll have an xcopy and installer version that will be much smaller and easier to extract the provider from.
Any day now. Trying to fix the last set of bugs before delivering ODAC 12c.
If you want to comment on ODP.NET Nuget support, you can post to this thread on that topic. I would be interested in hearing any feedback you have, especially whether a generalized vendor supplied ODP.NET Nuget package would be useful on its own.