docs: explain signal object and array updates - #1627

Changed pages include:

• index.html - view
• quick-start.html - view
• solid-meta.html - view
• solid-router.html - view
• advanced-concepts/fine-grained-reactivity.html - view
• concepts/context.html - view
• concepts/effects.html - view
• concepts/intro-to-reactivity.html - view
• concepts/refs.html - view
• concepts/signals.html - view

There are more changes not included in the list