Docs: Link to Go Client documentation

[jimpick]

All of the JSON-RPC methods callable from the Go client are listed here:

https://github.com/filecoin-project/lotus/blob/master/api/apistruct/struct.go

Godoc.org automatically publishes any inline documentation, for example:

• https://godoc.org/github.com/filecoin-project/lotus/api/apistruct

The methods are currently lacking the comments that godoc uses. Here is a blog post describing how to document go code:

https://blog.golang.org/godoc

The JS Client documentation will probably share many descriptions with the go and JSON-RPC documentation. Ideally there would be an easy way to jump to the go documentation for a particular method from the JS documentation. This might be particularly helpful in the beginning before the entire API has been wrapped.