feat: add advice list to error health check

[Agent-E11]

There is an optional advice parameter to the error function in vim.health. This is a list of suggestions for the user. This could be something like:

local advice = {
  "If on Termux: Install Termux:API (url: ...)",
  "If on Linux: Install acpi",
  "If on MacOS: Install `pmset`", -- Is this supposed to be installed already?
  "If on Windows: I have no idea..., powershell should just work",
  "If nothing is working for you, create an issue at github.com/justinghj/battery.nvim/issues/new",
}