docs(readme): make bootstrap snippet work well with lua-language-server

[saccarosium]

Hi,
this PR tries to:

• make the bootstrapping snippet work a bit nicer with lua-language-server. lua lsp will complain about the use of vim.fn.stdpath in vim.fs.joinpath since it can return string[] and will throw a warning. The fix is telling it to treat the stdpath call as a string.
• make the bootstrapping snippet less intimidating by reducing is sice in LOC
• remove redundant vim.fs.normalize call (vim.fs.joinpath already does that`)
• move the vim.v.shell_error check in the same branch as a "sanity check". It is nitpicking but, as is it right now, this can be trigger by any vim.fn.system or :! gone wrong in the user configuration and moving it to the same branch as the vim.fn.system call that clones the repo this can make life much saner to user.

[github-actions]

Review Checklist

Does this PR follow the Contribution Guidelines? Following is a partial checklist:

Proper conventional commit scoping:

• For example, fix(installer): some installer bugfix

• Pull request title has the appropriate conventional commit prefix.

If applicable:

• Tested
  • Tests have been added.
  • Tested manually (steps in PR description).
• Updated documentation.

[mrcjkb]

Hey 👋
Thanks for your PR 🙏

remove redundant vim.fs.normalize call (vim.fs.joinpath already does that`)

That is incorrect. joinpath (as of writing) only does gsub('//+', '/'), which is less than normalize.

Please also revert your change to the joinpath arguments. Right now, joinpath adds a / on all platforms, but that could change.

Please also refer to the review checklist, specifically regarding the use of conventional commits.

[saccarosium]

That is incorrect. joinpath (as of writing) only does gsub('//+', '/'), which is less than normalize.

Interesting, I was basing this on the documentation. I didn't actually read the implementation. I should have done it...

Concatenate directories and/or file paths into a single path with
normalization (e.g., "foo/" and "bar" get joined to "foo/bar")
-- :h vim.fs.joinpath