Add jsonrpc dependency info

[tninja]

Based on

1. Using the latest commit(09c6005), Emacs will show error message when starting #232
2. Copilot.el stop working on Mac OSX recently #244

[tninja]

if there is a way to let copilot.el automatically install the dependency, it is much better than this.

[jcs090218]

What package manager are you using? The built-in package manager --- package.el will handle it for you. 🤔

[tninja]

What package manager are you using? The built-in package manager --- package.el will handle it for you. 🤔

Yes. Probably should replace ELPA to package manager.

[tninja]

Move the description to installation part beside the editorconfig package dependency.