config: nvim: use colorscheme dark_colorblind from github-nvim-theme

The currently used colorscheme 'vim-dichromatic' is missing support for
various neovim plugins.

config/nvim/lua/plugins/github-nvim-theme.lua

@@ -0,0 +1,4 @@
+require('github-theme').setup({
+	theme_style = 'dark_colorblind',
+	transparent = true,
+})

config/nvim/lua/plugins/nvim-cmp.lua

@@ -1,6 +1,4 @@
 vim.opt.completeopt = 'menu,menuone,noselect'
--- make 'kind' readable with dichromatic colorscheme
-vim.cmd('highlight! CmpItemKindDefault guibg=NONE guifg=#000000')
 
 local cmp = require('cmp')
 cmp.setup({