Add docs about the emacs-client and how to configure it

[opti-mix]

Thanks for including the emacs-client!

It would be nice mention the emacs-client in the docs/README.

It would also be helpful to provide an example of what needs to be added to Emacs config to start using this client.

Which key combinations/commands one should use when editing the file to trigger the auto-completion, etc?

If this client is known to have conflicts with some other popular Emacs modes like e.g. ycmd or company-clang, it would be useful to mention what needs to be disabled or configured differently to make sure that cquery emacs client is used.

These emacs-client specific docs could be probably placed in the emacs sub-directory, together with the client's source code.

@topisani You are probably the best candidate for providing this information, or? :-)

[topisani]

yeah definately - the emacs client is still very experimental, and for example it currently breaks most other lsp-mode clients when you have it loaded (not started, just the file loaded). But yep, we definately need docs, though id rather do them in a week or so when its a bit more stable, and less likely to break.

[MaskRay]

There is now a wiki page https://github.com/jacobdufault/cquery/wiki/Emacs
Feel free to contribute to it!