Docs: Link to JSON-RPC method documentation

[jimpick]

The low-level Lotus JS Client RPC library method calls with have a 1:1 relationship with the exported JSON-RPC methods, so will shared much documentation in common (description, parameters, output, etc.). It would be good to link from the JS Client Docs to the documentation for the JSON-RPC methods.

Open Work Labs has done some preliminary work using Postman to document a subset of the JSON-RPC methods:

https://documenter.getpostman.com/view/4872192/SWLh5mUd?version=latest