Allow style customizations

[paganotoni]

After some conversations, I've come to think the following strategy is doable:

• When doco init is invoked, it would generate a styles.css file with default styles.
• When generating doco will
  • Look for styles.css in the source folder
  • If found, use it
  • Otherwise, use its default tailwind style.

This implies we should add some IDs to make elements easier to reference and customize. A few of the side things this should cover are:

• Documenting how to do it
• Customize some things in the doco website as an example.