Document how to run ctags with custom settings

[kisabaka]

Zoekt supports starting a custom ctags binary which can be useful when the default settings cause ctags to fail (e.g when a language isn't available on the host system)

[kisabaka]

@keegancsmith improving the ctags docs to get past issues like this: sourcegraph/go-ctags#6

[keegancsmith]

These are quite detailed instructions. We already mention the name of the package in the current description. I think it would be better for us to just implement the linked issue. But we should also bump the version of ctags we use to be honest and adjust the language list accordingly :) I'll do the latter today.

[kisabaka]

That sounds good to me! I ran into the issue with this version of ctags:

$ universal-ctags --version
Universal Ctags 0.0.0, Copyright (C) 2015 Universal Ctags Team
Universal Ctags is derived from Exuberant Ctags.
Exuberant Ctags 5.8, Copyright (C) 1996-2009 Darren Hiebert
  Compiled: Jan  6 2019, 23:23:29
  URL: https://ctags.io/
  Optional compiled features: +wildcards, +regex, +iconv, +option-directory, +xpath, +json, +interactive, +sandbox, +yaml