feat(colorscheme): add nord (#186)

* feat(colorscheme): add nord

* fix: linting

* fix(nord-nvim): requested README changes

* fix(nord-nvim): formatting

* fix:(nord-nvim): use correct repo name...

* fix(nord-nvim): correct scoping of opts vars

* fix(nord-nvim): remove unnecessary setting, this is handled by the colorscheme being set

---------

Co-authored-by: Micah Halter <[email protected]>

lua/astrocommunity/colorscheme/nord-nvim/README.md

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+# nord.nvim
+
+**Repository:** <https://github.com/shaunsingh/nord.nvim>
+
+Neovim theme based off of the Nord Color Palette, written in lua with treesitter support
+
+## Customization
+
+To support [headlines](https://github.com/lukas-reineke/headlines.nvim), you should add this code to your config:
+
+```lua
+local utils = require("astronvim.utils")
+{
+  "lukas-reineke/headlines.nvim",
+  opts = function(_, opts)
+    if not opts.markdown then opts.markdown = {} end
+    opts.markdown.headline_highlights = utils.list_insert_unique(opts.markdown.headline_highlights, {
+      "Headline1",
+      "Headline2",
+      "Headline3",
+      "Headline4",
+      "Headline5",
+      "Headline6",
+    })
+    opts.markdown.codeblock_highlight = utils.list_insert_unique(opts.markdown.codeblock_highlight, "CodeBlock")
+    opts.markdown.dash_highlight = utils.list_insert_unique(opts.markdown.dash_highlight, "Dash")
+    opts.markdown.quote_highlight = utils.list_insert_unique(opts.markdown.quote_highlight, "Quote")
+  end,
+},
+
+```
+
+To support [BufferLine](https://github.com/akinsho/nvim-bufferline.lua), you can add this code to your config:
+
+```lua
+local utils = require("astronvim.utils")
+{
+  "akinsho/bufferline.nvim",
+  opts = function(_, opts)
+    if not opts.options then opts.options = {} end
+    opts.options = utils.list_insert_unique(opts.options, {
+      separator_style = "thin",
+    })
+
+    local highlights = require("nord").bufferline.highlights({
+      italic = true,
+      bold = true,
+    })
+
+    opts.highlights = utils.list_insert_unique(opts.highlights, highlights)
+  end,
+}
+```

lua/astrocommunity/colorscheme/nord-nvim/nord.lua

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+return {
+  "shaunsingh/nord.nvim",
+  init = function()
+    vim.g.nord_contrast = true
+    vim.g.nord_borders = false
+    vim.g.nord_disable_background = false
+    vim.g.nord_italic = false
+    vim.g.nord_uniform_diff_background = true
+    vim.g.nord_bold = false
+  end,
+}