docs: move minimum reproduction template from wiki to repo

Instead of a markdown file, just use a lua file instead that users can
use directly.

contrib/minimal.lua

@@ -0,0 +1,14 @@
+-- Run this file as `nvim --clean -u minimal.lua`
+
+for name, url in pairs{
+  -- ADD PLUGINS _NECESSARY_ TO REPRODUCE THE ISSUE, e.g:
+  -- some_plugin = 'https://github.com/author/plugin.nvim'
+} do
+  local install_path = vim.fn.fnamemodify('nvim_issue/'..name, ':p')
+  if vim.fn.isdirectory(install_path) == 0 then
+    vim.fn.system { 'git', 'clone', '--depth=1', url, install_path }
+  end
+  vim.opt.runtimepath:append(install_path)
+end
+
+-- ADD INIT.LUA SETTINGS _NECESSARY_ FOR REPRODUCING THE ISSUE