[FR]: Document installation using Lazy

[Bubobubobubobubo]

Hi, I have switched my config to Lazy and always encounter troubles when occasionally re-installing scnvim. Nothing dramatic, but the way I install it is a bit baroque. I don't have an extensive knowledge of the Neovim internals. I'm able to get it working by tweaking my init.lua but not following the workflow that Lazy (partially) enforces.

Describe the solution you'd like

I'm suggesting the addition of a few lines in the README.md file to document the installation process with more package managers, including Lazy. There are a few lines about this already on the forum.

Describe alternatives you've considered

I have not considered any alternative since I am not really having an issue with scnvim itself.

Additional context

This is how I always end up installing it:

1. adding the plugin the Lazy way:

  {
    'davidgranstrom/scnvim',
    name = 'scnvim',
    priority = 1000,
    opts = {
      editor = {
        highlight = {
          color = 'IncSearch',
        },
      },
      postwin = {
        float = {
          enabled = false,
        },
      },
    },
  },

2. manually pasting everything else at the bottom of the file, without really thinking twice.

local scnvim = require 'scnvim'
local map = scnvim.map
local map_expr = scnvim.map_expr
scnvim.setup {
  keymaps = {
    ['<M-e>'] = map('editor.send_line', { 'i', 'n' }),
    ['<C-e>'] = {
      map('editor.send_block', { 'i', 'n' }),
      map('editor.send_selection', 'x'),
    },
    ['<CR>'] = map 'postwin.toggle',
    ['<M-CR>'] = map('postwin.toggle', 'i'),
    ['<M-L>'] = map('postwin.clear', { 'n', 'i' }),
    ['<C-k>'] = map('signature.show', { 'n', 'i' }),
    ['<F12>'] = map('sclang.hard_stop', { 'n', 'x', 'i' }),
    ['<leader>st'] = map 'sclang.start',
    ['<leader>sk'] = map 'sclang.recompile',
    ['<F1>'] = map_expr 's.boot',
    ['<F2>'] = map_expr 's.meter',
  },
}

I can probably help with a PR when I'll have spare time to debug my computer :)