[docs] "Misleading" Alert title in the first example

[igorsantos07]

Hello there!

I'm using sveltestrap for a quick pet project and I've been doing quick doc glances... This issue was specially striking for me, but I didn't find an easy way to edit the Storybook (never used these before).

Thus...

1. I would suggest adding some help guide on how to contribute to the docs :)
2. replace that misleading <h4 class="alert-heading text-capitalize">{color}</h4> with a heading={color} prop; if you just check the first example (which is mostly feature-complete, besides that), you'll think there's no title element whatsoever and you must write an h4 by yourself.