README: document that repo name changed back to go (from go-codec)
README: document that repo name changed back to go (from go-codec)

Tools like Travis-CI, etc had issues when the package import path differs
with the repo name.

We have now undone the repo name change.

This shouldn't affect anyone, since go get expects the original name anyway.

ugorji/go,ugorji/go,ugorji/go