Add nv-cmp sources step to installation instructions

[Mike Kent]

Hi all,

I'm setting up nvim + cody for the first time and it took me forever to figure out that the reason I wasn't getting suggestions was because "cody" was not setup as an nvim-cmp source (I'm also new to nvim-cmp). I tried everything else from "sourcegraph" and "sg", but never considered "cody" until I found it from the source code here. It would have saved me multiple hours if this was listed as part of the installation instructions in the readme and/or on SourceGraph's site.

Hope this can help others, thanks!

[TJ DeVries]

Thanks, I added the info here: 691e138

Good call out :) I had it in the docs for the plugin, but should link in the readme.