config: add a minimal config for Markdown

- Add a minimal configuration for Markdown demonstration, with only the
  markdown preview, has it is to demonstrate the syntax.
- Uncomment the adwaita theme in the minimal config (minit.lua).
- Set another keymap to open the nvim-tree column, has the one used till
  now is conflicting with diagnosis management.

Co-Authored-by: iGor milhit <igor@milhit.ch>

lua/plugins/nvim-tree.lua

@@ -19,7 +19,7 @@ return {
     -- <leader>e to toggle the explorer buffer 
     vim.keymap.set(
       "n",
-      "<leader>e",
+      "<leader>n",
       "<cmd>NvimTreeFindFileToggle<CR>",
       { desc = "[nvim-tree] Toggle the file explorer" }
     )

md.lua

@@ -0,0 +1,55 @@
+-- TODO: Rewrite it accordingly to new configuration.
+-- TODO: Also, make it actually minimal. 😉
+
+-- Set <space> as the leader key
+-- See `:help mapleader`
+--  NOTE: Must happen before plugins are required (otherwise wrong leader will be used)
+vim.g.mapleader = ' '
+vim.g.maplocalleader = ' '
+
+-- Minimal options
+--  Display relative line numbers
+--  Except to the active line
+vim.opt.relativenumber = true
+vim.opt.number = true
+
+-- Enable mouse mode
+vim.opt.mouse = 'a'
+
+-- Install package manager
+--    https://github.com/folke/lazy.nvim
+--    `:help lazy.nvim.txt` for more info
+local lazypath = vim.fn.stdpath 'data' .. '/lazy/lazy.nvim'
+if not vim.loop.fs_stat(lazypath) then
+  vim.fn.system {
+    'git',
+    'clone',
+    '--filter=blob:none',
+    'https://github.com/folke/lazy.nvim.git',
+    '--branch=stable', -- latest stable release
+    lazypath,
+  }
+end
+vim.opt.rtp:prepend(lazypath)
+
+require('lazy').setup({
+
+  {
+    "Mofiqul/adwaita.nvim",
+    lazy = false,
+    priority = 1000,
+    config = function()
+      vim.cmd('colorscheme adwaita')
+    end
+  },
+  {
+    "iamcco/markdown-preview.nvim",
+    ft = {
+      'pandoc',
+      'markdown',
+    },
+    lazy = true,
+    build = "cd app && npm install && git reset --hard",
+  },
+
+})

minit.lua

@@ -34,13 +34,13 @@ vim.opt.rtp:prepend(lazypath)
 
 require('lazy').setup({
 
-  -- {
-  --   "Mofiqul/adwaita.nvim",
-  --   lazy = false,
-  --   priority = 1000,
-  --   config = function()
-  --     vim.cmd('colorscheme adwaita')
-  --   end
-  -- },
+  {
+    "Mofiqul/adwaita.nvim",
+    lazy = false,
+    priority = 1000,
+    config = function()
+      vim.cmd('colorscheme adwaita')
+    end
+  },
 
 })