docs: suggest leveraging vite static asset handling for theme files

[NickantX]

Vite's Static Asset Handling can be helpful to mention in the instructions for theming SMUI. Notably, it solves the problem of stale caches after you deploy an updated SMUI theme for your application. I've included it here as a separate option rather than removing anything else, since not everyone is using Vite, but it is the default for new SvelteKit apps.